(Washingion D.C) Fortune -- On a wretchedly hot August day outside the Caterpillar tractor plant in Montgomery, Ill., President Bush and the state's congressional delegation gather for the signing of the massive transportation bill. This is 2005, the calm before the Katrina storm, and a rigorous mountain-biking schedule has the President in top shape.

In off-camera chitchat with the shirt-sleeved lawmakers, Bush takes note of Democratic Congressman Rahm Emanuel's deep tan, prompting the 46-year-old Emanuel to boast about the miles of swimming and biking in his triathlon training schedule. Testosterone oozes into the humid air space between the two men. Bush invites Emanuel down to Texas to do some real biking. "So I said, 'I'll make you a deal, Mr. President. I'll bike if you swim.' Now he didn't exactly say swimming was a wussy sport, but you could tell.... So I said, 'Mr. President, Laura can put your water wings next to the lake. You can have your water wings.' "

More from Fortune Hedgie's careful prescription for profiting in the mortgage mess A goal we can believe in Rahm Emanuel: Pit bull politician FORTUNE 500 Current Issue Subscribe to Fortune

At that point you might think this graduate of the Evanston School of Ballet-a man whose office features sunset photos and who has the mellow chords of David Gray playing on his iPod-would leave well enough alone. But Emanuel is hard-wired to go for the jugular: Politics Chicago-style are part of his DNA. So he sharpens his drill bit on the leader of the free world. "I said to him, 'You're not one of those tribathletes, are you, Mr. President? You know-steam, sauna, shower?'

"And Bush goes, 'That's g-o-o-d.' "

Eyes dancing, Emanuel spins that last word with a solid impersonation of the President's Midland drawl. He is recounting this story 11 months later, from an office overlooking a construction site and a freeway, four blocks from the leadership offices of the U.S. Capitol he hopes to occupy some day. He has just returned from the House floor, taut and unable to sit still, his kinetic brain consumed by an upcoming election that will affect the personal fate of both men.

Banter with a U.S. President is nothing new to Emanuel; he was at Bill Clinton's side as a political advisor inside the White House for six years and still talks strategy with him at least once a month. Now chair of the Democratic Congressional Campaign Committee-the operations center for House candidates (Washington nickname: "D-Triple C")-Emanuel is applying rugged business discipline to the Democratic Party's historic effort to wrest control of the U.S. House from the Republicans. Last year he recruited dozens of candidates to challenge GOP incumbents. This year he is holding feet to the fire to raise record amounts for the Democrats' effort.

Along the way Emanuel has widened his core of admirers-and made powerful enemies. Nervous about being swamped by Republican money this fall, he spent the summer locked in a bitter dispute with Democratic National Committee chair Howard Dean over the allocation of election resources-the political equivalent of Microsoft executives arguing over how many Xboxes to ship where for the Christmas season.

In private Emanuel told off Dean. In public he's aimed similar messages at liberal financiers like George Soros for being stingy and at the leftist activists in MoveOn.org for being ineffective. "Is there anyone Rahm Emanuel isn't fighting with?" asks a MyDD blogger. A straw poll by another leftist blog, Daily Kos, gave Emanuel a 58% disapproval rating.

All this matters, of course, only if the Democrats lose. "Holy Christ, his butt is on the line," says Democratic strategist Paul Begala, who describes Emanuel's aggressive style as a "cross between a hemorrhoid and a toothache." Begala continues, "I love Rahm, but that's a small group of us. He's not a beloved figure like Tip O'Neill or Dick Gephardt. Rahm's there because they want to win."

If Emanuel does succeed in returning House Democrats to power for the first time in 12 years, it's a safe bet that this one-time investment banker will vault up the House leadership ranks and eventually be in a position to bid for the Speaker's title that Chicagoans once hoped would be held by their legendary Dan Rostenkowski.

Hillary Clinton may or may not become the party's presidential nominee. Howard Dean and Nancy Pelosi may or may not remain the GOP's favorite tetherballs. But Emanuel-now only 47 years old and in a safe district-is fast emerging as a new force in the Democratic Party.

He also symbolizes the party's painful internal divisions. He is praised by Democratic strategists who think the party needs to resist moving left (nearly twice as many American voters call themselves conservative as call themselves liberal) and distrusted by some in the party's liberal wing. He considers Connecticut Senator Joseph Lieberman a good friend, even though Lieberman's support of the Iraq war inflamed leftist sentiment and cost him his party's nomination.

"We have two Democrats running," Emanuel says, referring to Lieberman, now campaigning as an independent, and primary winner Ned Lamont. Emanuel himself criticizes Bush's conduct of the war but not the original decision to topple Saddam Hussein.

Still, even the most liberal activists admire Emanuel's martial instincts. Borrowing Newt Gingrich's battle cry that politics is "war without blood," Emanuel has come out swinging, determined to avoid a replay of the timid, flip-flopping mess that was the 2004 campaign.

Former President Clinton told FORTUNE he considers Emanuel "one of the top political minds in Washington," a strategist who "favors the counterattack over the attack." Clinton adds: "His politics are rooted in new ideas and old-fashioned values." Former Bush economic advisor Douglas Holtz-Eakin, who, as Congressional Budget Office director, worked with Emanuel, calls him the "real deal." (Like Rostenkowski, Emanuel has a seat on the powerful Ways and Means Committee.)

This "real deal" is not your average back-slapping, fraternity-brother brand of politician. You'll find him watching Twyla Tharp choreography, not his golf swing, even as he's calculating how to slash his opponent. "He will step into a fight and not back down easily, if at all. He doesn't mind the heat," says his equally combative little brother, Hollywood superagent Ariel Emanuel.

Emanuel has rejuvenated the hopes of House Democrats in no small part by applying the money-raising acumen he used when Clinton's 1992 presidential campaign nearly sank under the weight of Gennifer Flowers' accusations. With a penchant for networking and making deals-honed during a stint at Wasserstein Perella (which netted him more than $18 million in just over two years)-Emanuel has put the party's House campaign coffers on a par with the Republicans' for the first time in years.

Conservative Republican Tom Cole, a U.S. Representative from Oklahoma, cited Emanuel's ferocity in a recent letter to colleagues asking for their support in his own campaign to run the counterpart House GOP operation next term. "He's dangerous," says Cole, who calls Emanuel a friend. "He has a closing intensity. When he's got a political kill in sight, he's absolutely relentless." And that, says Cole, has the GOP worried this fall.

On a Tuesday afternoon in june, inside a Capitol Hill conference room, the Democratic Party's three biggest moneymen take their places around an oval table to begin a session of dialing for dollars. New York's camera-ready but frumpy senior Senator, Charles Schumer, tosses off his shoes, puts up his feet, and starts cracking jokes. Former DNC chair Terry McAuliffe walks in, all toothy grins. Emanuel, trim and 5-foot-8, by far the smallest of the trio, is by contrast hyperserious. Between donor calls he barks at staff and clicks out messages on his BlackBerry, according to people in the room.

"Hey, Tommy," Schumer deadpans into the speakerphone once superlobbyist Tommy Boggs is connected, "have I got an opportunity for you!"

"I think I'd rather have my proctologist calling," Boggs quips. The trio wants Boggs to bring in $100,000-$25,000 per donor-for an October fundraising dinner at the Clintons' Washington, D.C., home. Boggs pleads that he's already given to Schumer's senatorial committee.

"That was breakfast, Tommy," Schumer laughs. "This is dinner."

The Clinton event-to be followed by lunch with congressional leaders-is part of the Democrats' "last-minute money," a cash hoard they are building to return fire when Republicans start upping the money ante. As the fall campaign clicks into high gear, Democratic strategists say they have at least a fifty-fifty chance at taking back the House. "It's a jump shot," says Maryland Congressman Chris Van Hollen, one of Emanuel's top DCCC lieutenants.

But Democratic prospects could easily sour if the Republicans pour in last-minute millions that they can't match. That possibility is fueling tensions between DNC chair Dean and Emanuel. One month earlier, at a meeting on Capitol Hill, Emanuel and Schumer asked Dean to match the Republican National Committee's expected outlay in the fall campaign. Dean refused to budge from what he describes as a long-term financial strategy to build up the party in all 50 states. As Dean balked at Emanuel's money demands, tempers flared, and the Chicago Congressman couldn't contain his. He stormed out, lobbing one of his famed "f-bombs" at Dean.

Within weeks, according to sources close to the fracas, Schumer was trying to reopen communication with Dean-sans the hot-tempered Emanuel-while Emanuel was firing off a letter to Dean demanding $100,000 for each of some 40 targeted races and pointing out that Gingrich's famed 1994 GOP takeover of the House was backed by $20 million in RNC funds. When news of the letter leaked to the press, anonymous Dean supporters accused Emanuel of laying the groundwork to shift the blame if the Democrats lose in November.

Emanuel's fears about being slaughtered by RNC money are legitimate. A deal he brokered with Dean in early September committed the DNC to spend $2.4 million on 40 competitive House races, while the RNC will be drawing on a war chest that will probably clock in at 25 times that size. But ego is also part of this intraparty fracas: Schumer and Emanuel are both seasoned victors-Schumer beat powerful Republican Senator Al D'Amato; Emanuel advised a winning presidential candidate before beating a Polish Catholic in a majority Polish Catholic district in his own race for Congress.

Emanuel-Schumer allies view Dean as a hand-me-down governor (he took over in Vermont when his predecessor died) of a tiny cheese state who blew up his quixotic 2004 presidential campaign by blowing through his money.

Emanuel and Schumer schmooze easily with the silk-thread Wall Street crowd. Dean is a practiced outsider. Emanuel and Schumer pride themselves not only on breaking fundraising records but on running lean operations and saying no to incumbent candidates who don't need their help.

"Chuck is tighter than a tick, and so is Rahm," says Hassan Nemazee, a New York investor who chairs national fundraising for Senate candidates. Dean behaves more like a governor, broadly doling out money to build staff and operations.

As I arrive for a July interview with Emanuel at DCCC headquarters, former Gore campaign chief Donna Brazile is standing on the sidewalk, buttonholing him. A party veteran, Brazile has seen more than her share of internal Democratic Party squabbles, and she's worried about this one.

Some party activists view Emanuel as the instigator of a feud that is dividing the party. Dean may be the object of sighs and eye-rolling by pragmatic, big-donor Democrats-the crowd that has generally signed on with Emanuel-but as a populist hero to party activists and the "netroots" he helped spawn, the former presidential candidate has his own powerful base. So Brazile tells me she is here to deliver a compromise plan she hopes will cool the fires between the two men.

Minutes later, upstairs in his office, Emanuel obliquely suggests that Dean is nearly as big an obstacle as Karl Rove to a Democratic win. "Everyone is pulling their weight," he says, with the implication that Dean-whose DNC has $11 million in cash, compared with the RNC at $43 million-is the exception.

"Eleven of our challengers have nearly, or more than, a million dollars cash on hand. In 2004 it was zero. Zero." He shoots the last word out like a golden fireworks spray, letting it settle for effect before continuing. "I have no problem with building for the long term. But I don't know another way to win when the other side has $40 million. They got a cavalry. We need a cavalry."

Yet Dean is hardly the only one on Capitol Hill annoyed with Emanuel-so are some of the House members he is horse-whipping when they fail to pay their DCCC dues. "Nothing replaces perspiration," he says of fundraising. "You set a goal and you drive toward that goal and you put everything toward it."

Every day, including weekends, he makes calls to donors, calls to candidates to remind them to call donors, callbacks if he doesn't get an answer-or if he gets the wrong one. Says Boggs: "There's no hesitancy about asking for money and then arguing with you if he thinks you're not giving enough. If you won't take his call at 4, he'll call at 4:15; if you don't take it then, he'll call at 4:30."

Emanuel wasn't the brains of his family-that was his older brother, Ezekiel, who would grow up to become an oncologist and one of the nation's leading bioethicists. Nor was he the brawn-that was younger brother Ariel, whose raw combative style is so legendary in gladiatorial Hollywood that he was the inspiration for the hyper-ruthless, Viagra-popping agent Ari Gold in the HBO series Entourage.

Rahm was the one dancing through the living room to his mother's jazz and classical music, spinning pirouettes and leaping down the stairs of his family's suburban Chicago split-level. A popular kid but not especially focused, he had none of that out-of-the-womb political ambition so evident in the lives of leaders like Bill Clinton.

And then he almost died. With high school graduation days away, Emanuel sliced his finger while working in a fast-food joint. Infection took hold after a prom-night swim in Lake Michigan. By the time this son of a pediatrician finally sought medical care, he was suffering from a severe blood and bone infection. He lay in the hospital, his temperature reaching 106. Marsha Emanuel, his mother, is a force of will-a woman who can compare the insides of the Evanston and Chicago prisons based on her three arrests at civil rights protests. But on this subject tears still well up in her hazel eyes. "We almost lost him," she says.

After a six-week battle, he recovered, losing half his finger to the infection but gaining a new sense of seriousness and purpose. "He has one of the strongest survival instincts I've ever seen," says longtime friend Mary Leslie, who attributes that inner reserve to his Israeli roots. His father, Benjamin, was born in Jerusalem, the son of pharmacists who had escaped the Russian pogroms. In the 1940s Benjamin Emanuel interrupted his medical school training in Switzerland to take part in an unsuccessful scheme to smuggle guns from Czechoslovakia to the Israeli underground. He later served as a medic in the 1948 Israeli war of independence. (Rahm would echo his father's dedication during the Gulf war: With Iraqi Scuds falling on his father's home country, he volunteered for military-vehicle-maintenance duty near the Lebanese border.)

In 1953, Dr. Emanuel's medical training brought him to the States, where he met Marsha, then an X-ray technician at Chicago's Mount Sinai hospital. They married and, after a brief return to Israel, settled down in Chicago. Dr. Emanuel's pediatrics practice on the North Side's Lincoln Avenue drew a passel of immigrants, and eventually became-with his partners-one of the largest in the city. (Decades later the "Doc's" families would turn out to vote for his son in a congressional election.)

Money was tight in the early years. The family left their first Chicago apartment because it was rat-infested. They were kicked out of their second apartment because tenants complained that the three rambunctious boys were too loud. Yet Chicago also meant a lively street life of playing hoops in the park and building go-carts in the alley with the artist who lived upstairs.

That came to an end when Rahm was 9 and their immigrant father achieved the American dream of buying a house in the suburbs, the lakeside Republican enclave of Wilmette. The boys, recalls brother Zeke, missed the city. "The suburbs never grafted on to us," he says.

The boys also joined their mother on most civil rights demonstrations within a 50-mile radius of Chicago. "I only brought the kids if I thought it was going to be peaceful, with no arrests," Marsha Emanuel insists. (Though it wasn't always predictable; she wore a dress and had a dinner party planned when she was carted off by cops for her first overnight jail term.)

Marsha's father was a burly Moldavian immigrant who arrived alone on a ship at age 10. He went on to become a union organizer. Politics-loud and argumentative-infused Marsha's childhood; her three boys got their own dose from trips in their grandfather's delivery truck.

Rahm jumped into politics right after his graduation from Sarah Lawrence College, where he promised his mother he would take advantage of the campus's stellar dance program but never did. He quickly discovered a penchant for fundraising, which he applied to campaigns for Senator Paul Simon, the DCCC, and Chicago's Mayor Richard Daley. In 1991 he joined Clinton's presidential campaign. Emanuel wowed the team from the start, opening a spigot on needed campaign funds, and after Clinton's election helped program a picture-perfect inaugural. He nabbed the plum White House position of political director.

Then he started shooting off his mouth. There was the time he rapped on a conference table to get "Lloyd's" attention. ("We were all aghast," recalls one Clinton aide, noting that even Lloyd Bentsen's wife still called the Treasury Secretary "Senator." ) He had a very public run-in with the late Senator Patrick Moynihan, who accused him of being the source of an anonymous quote that "we'll roll all over [Moynihan] if we have to" on welfare reform. (Emanuel denied saying it.) Most damaging were Emanuel's battles with Hillary Clinton loyalists, who accused him of leaks about the travel office episode.

A year after Clinton took office, Emanuel was demoted. "He was very upset," recalls Zeke. "He thought he was going to get kicked out of the White House." He didn't, and neither did he quit. Instead, Emanuel regrouped, helping lead the charge on key Clinton initiatives, including the crime bill, the assault weapons ban, and NAFTA. "He was constantly on the offense," says Begala. Emanuel planned to leave after the 1996 election, but Clinton promoted him to take George Stephanopoulos's spot as senior advisor for policy and strategy.

Still, Emanuel had political aspirations of his own, which necessitated some financial security. So in late 1998 he traded in Clinton as his boss for Bruce Wasserstein, a major Democratic donor and Wall Street financier. "Money is not the be-all and end-all for him," says brother Zeke. "But he knew he needed money so that wouldn't be a problem while he was doing public service." Over a 2 1/2-year period he helped broker deals-often using political connections-for Wasserstein Perella.

According to congressional financial disclosures, he earned more than $18 million during that period. His deals included Unicom's merger with Peco Energy and venture fund GTCR Golder Rauner's purchase of SBC subsidiary SecurityLink. But friends say his compensation also benefited from two sales of the Wasserstein firm itself, first to Dresdner Bank and then to Allianz AG.

By 2002, Emanuel emerged as a wealthy man with a reputation as a battle-hardened national strategist. That year he won a tough primary race for a seat in Congress that paid $138,000. His 1994 White House demotion was ancient history.

"There are people who never lose, who never fail, and their first failure is usually a disaster," says Zeke. "That is not characteristic of Rahm or anyone else in our family. What we're very good at-and what Rahm is very good at-is coming back. Persistence and picking yourself up off the floor and working harder and learning lessons from getting kicked in the teeth." In 2005 that's exactly what the long out-of-power Democrats decided they could use, and so they turned to Emanuel to run the DCCC.

Emanuel's in-your-face money demands make him stand out in a party that has sometimes been a little prissy about big-donor fundraising. "Republicans understand power and that you need money to get power. Our guys don't," complains one of the party's leading funders. Colleagues say Emanuel has become adept at the care and feeding of big donors-knowing their interests, asking about their families, sending them cheesecakes from Chicago's Eli's Bakery. He's expanded the DCCC's donor base, appealing both to like-minded young financiers and big-business donors with GOP ties who are hedging their bets this fall.

Emanuel shuttles between a turn-of-the-century house in Chicago (home to his wife, Amy Rule, who works with disadvantaged youth through art programs, and their three children) and a basement apartment on Capitol Hill, where he jokingly calls himself "the hobbit." In between, he's co-authored a Democratic agenda called The Plan with former Clinton policy advisor Bruce Reed-who calls himself "one of the few people in America that Rahm doesn't yell at." The Plan reflects much of the same centrist sensibility both men displayed at the Clinton White House.

Emanuel is drawn to issues that resonate with average voters, like stem-cell research, raising the minimum wage, and a "fair, flat" income tax. While Bush was pushing his Medicare drug plan, Emanuel was pounding the administration to permit drug imports from Canada-a popular cause for families facing high prescription bills.

On Iraq, Emanuel has steered clear of the withdraw-now crowd, preferring to criticize Bush for military failures since the 2003 invasion. "The war never had to turn out this way," he told me at one of his campaign stops. In January 2005, when asked by Meet the Press's Tim Russert whether he would have voted to authorize the war-"knowing that there are no weapons of mass destruction"-Emanuel answered yes. (He didn't take office until after the vote.) "I still believe that getting rid of Saddam Hussein was the right thing to do, okay?" he added.

When it comes to slicing and dicing his Republican foes, Emanuel applies a Chicago pol's sensibility that recalls that famous Untouchables line: "He pulls a knife, you pull a gun; he sends one of yours to the hospital, you send one of his to the morgue." Connecticut Representative Rosa DeLauro describes Emanuel as a "reflection of Chicago politics, ward politics. It's local, ethnic. You're not in a tea party." Colleague Ed Markey, a veteran House member from Massachusetts, says simply, "He's not a political romantic."

Mostly out of power for the past six years, the Democrats could use Emanuel's comeback instincts. So the match is a timely one. But what's driving Emanuel crazy right now is how little control he has over the party's future-or his own. "Can we get the right candidates?" he asks. "Yes, and we busted our balls recruiting and expanding the field. Can we raise the resources? Yes. Can we help on issues? Yes." But at the end of the day, he asks, "which way will the wind blow on Iraq? On energy prices? On the Middle East?"

"For a type-A personality like me, I hate that. I hate that," he says, his voice trailing off as he spins through a Capitol building hallway. "Your fate is out of your hands."