WASHINGTON » Not that he is competitive or anything, but one Friday evening, John D. Podesta, a top adviser to President Barack Obama, announced at a White House meeting that he would finish a 10-mile race that weekend in so many minutes. Needling Denis McDonough, the president’s chief of staff, Podesta added: "I don’t know what Denis is going to run."

Sure enough, Podesta finished in an hour and 26 minutes, beating McDonough, 21 years his junior, by six minutes. So as Podesta, 66, packed up his West Wing office last week, he jokingly blamed his departure on a subsequent loss.

"I knew it was time to look at leaving the White House when Denis McDonough beat me in 12K Jingle Bell race," he tweeted.

Wiry, ascetic, profane and relentless, John Podesta has become the Democratic Party’s marathon man in more ways than one. He helped save Bill Clinton’s presidency from the fires of scandal and impeachment. He spent the last year trying to salvage Barack Obama’s presidency from gridlock and malaise. And now he has handed in his White House pass to try to create a Hillary Rodham Clinton presidency from the ashes of her last failed campaign.

Perhaps no other unelected Democrat has shaped his party as much during the last two decades. As Clinton’s chief of staff, as founder of the left-leaning Center for American Progress and most recently as Obama’s counselor, Podesta has pushed his party toward a more aggressive approach to both policy and politics.

"He’s a competitive cat," McDonough said.

Podesta will need that competitive streak if he becomes chairman of Hillary Clinton’s presidential campaign, as expected. It will fall to him to impose discipline on the sprawling and fractious Clinton universe, including the candidate and her famously undisciplined husband. And it will fall to Podesta to manage relations between an outgoing president focusing on his legacy and his would-be successor focusing on the next election.

"He believes in and uses power in a way that many Democrats are too pusillanimous to do," said Paul Begala, a former Clinton White House aide and longtime friend. "He’s not afraid to use power, and ruthlessly if necessary. I think he’s as good a political guy as I’ve ever seen. He’s the real thing."

To many Democrats, last week’s blowup over fundraising practices in the Clinton orbit emphasized the need for adult supervision, recalling the internal strife that helped doom Hillary Clinton’s primary bid against Obama seven years ago. Her 2008 campaign was riven by clashing rivals more intent on fighting each other than opposing candidates. For months, no single aide was truly in charge.

In recruiting Podesta, Clinton is signaling that she will impose a more orderly structure this time.

"When John speaks, both longtime Clinton supporters like me and people new to the circle will know that he’s speaking for her," said Harold Ickes, a top adviser to both Clintons for years. "That’s very important. That didn’t happen in 2008, with some of the resulting consequences."

No one doubts Podesta’s toughness. During his previous White House stint, colleagues joked that he was sometimes replaced by his evil twin "Skippy." And as someone who met Bill Clinton during a Senate campaign in Connecticut in 1970, he is one of the few people with the longevity and stature to talk bluntly with them when they mess up.

"The fact that he’s saying it would carry an enormous amount of weight," Ickes said. "Both of them consider him a very straight shooter."

Republican operatives view Podesta as a liberal who will tug Clinton away from the political center and make it harder for her to argue that she represents a fresh start after Obama’s administration.

"You’ve got to admire someone willing to move from one sinking ship to another that’s taking on water before it’s even left port," said Michael Short, a spokesman for the Republican National Committee. "Voters overwhelmingly don’t want a third term for President Obama’s liberal agenda, but it’s clear that’s what Hillary Clinton and John Podesta intend to give them."

Podesta, who declined to be interviewed because he is "superstitious" about profiles, was born in Chicago to an Italian-American father and Greek-American mother. His father never finished high school and worked in factories, pushing his children to go to college. While Podesta is a practicing Catholic like his father, he embraces his mother’s side as well, displaying Greek Orthodox icons in his White House office and adopting her love of cooking.

He has attributed his drive and temper to an ethnic upbringing during which yelling at the dinner table over politics was acceptable.

He came of age in the tumult of the 1960s. While studying at Knox College in Illinois, he and other students "debated, ranted, chanted, protested," as he put it in a 1998 commencement address, and he campaigned for Eugene McCarthy, the anti-war presidential candidate, in 1968.

Podesta earned a law degree from Georgetown University, where he still teaches on the side, and went to work for figures like Sens. Patrick J. Leahy of Vermont and Tom Daschle of South Dakota. With his brother, Tony Podesta, he founded the Podesta Group, which has become a powerhouse lobbying firm with extensive corporate ties.

After going to work for President Bill Clinton, he rose to chief of staff, presiding over a White House rocked by revelations about the president’s sexual adventures with Monica Lewinsky. To keep the staff focused on business, he threatened to fire anyone caught talking about the scandal.

But he understood before colleagues did that they would lose a House vote on impeachment despite popular support for Clinton, and he oversaw a strategy emphasizing the partisanship of the process to delegitimize the House vote and win a largely party-line acquittal in the Senate.

After leaving the White House, Podesta founded the Center for American Progress, a hybrid organization that married policy and politics.

"He’s a policy wonk’s policy wonk," said Sarah Rosen Wartell, a co-founder who added that he was also "very much a doer."

Enlisting wealthy donors like George Soros and Herb and Marion Sandler, Podesta made the center, and himself, power players in liberal politics.

In 2008, Obama tapped Podesta to run his transition, to the chagrin of the loyalists who had helped beat Hillary Clinton for the nomination. Obama tried to recruit him to join the administration, an entreaty he resisted until early 2014 when the presidency was flailing and he agreed to come on board for a year to help turn it around.

Podesta came with a strategy he and Wartell had outlined in a 2010 report about how a president could use his executive authority more aggressively without waiting for Congress. He also took on select projects, notably climate change and privacy in a big-data world.

For McDonough, the chief of staff now occupying the corner office with the patio and the fireplace that once belonged to Podesta, having a predecessor around, "a guy who’s seen it all," proved a benefit.

"John is always thinking a couple steps ahead," McDonough said.

Passionate about environmental issues, Podesta used his perch to help advance new regulations on power plants, negotiate a carbon reduction agreement with China, create the world’s largest marine refuge in the Pacific Ocean and protect stretches of Alaskan waters and wildlife refuge from drilling.

"It’s not clear to me he slept," said Carol M. Browner, formerly Obama’s top environmental adviser.

In a series of tweets on Friday listing his 10 favorite memories in the Obama White House, he devoted half to environmental issues. A longtime aficionado of extraterrestrial lore – he kept a little shrine to "The X-Files" in his Clinton White House office – he also wrote that "my biggest failure of 2014: Once again not securing the disclosure of the UFO files. thetruthisstilloutthere."

If he cannot find proof of alien life, then he will test the maxim that an outgoing two-term president and his party’s nominee always end up at odds. Al Gore did not want Bill Clinton campaigning for him in 2000, just as Sen. John McCain did not want George W. Bush campaigning for him in 2008.

Podesta may serve as a bridge between Obama and Hillary Clinton, hoping to ease the natural frictions that arise as a candidate tries to distinguish herself from a president with improving but still mediocre poll numbers. He has played the role before.

He negotiated on Obama’s behalf an agreement with Bill Clinton to limit his international activities while Hillary Clinton served as secretary of state. And later, when Bill Clinton went to North Korea to free two Americans, the White House sent Podesta along to keep tabs.

For the next two years, as he races another marathon as Hillary Clinton’s top adviser, Podesta will have the advantage of the relationship he forged with McDonough, Obama’s top adviser.

"He’s a great runner," McDonough said. "The guy’s made me much better at everything I do in this job. And he’s made me a better runner, too."

Peter Baker, New York Times

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