Summer is here, and Democrats in Washington are smiling again. In the bleak days of late winter and early spring, many a dispirited Dem felt overwhelmed by an unexpectedly nimble Bush administration. Predictions that the quirky election that put him into office would make Bush an impotent leader fizzled fast. In his first 100 days, Bush notched one success after another–from the confirmation of John Ashcroft, to a well-managed crisis with China, to passage of a tax cut the size which was considered unthinkable just a few months ago.

Now, having reclaimed control of the Senate (thanks to Vermont’s party-switching Jim Jeffords), Democrats are forcing Bush onto their turf of prescription drugs, HMO reform, the minimum wage, and more. They’ve also battered Bush with attacks on his environmental record and energy plan–and are getting set to roast him if his tax cut fails to invigorate the economy. Bush’s approval rating had fallen to a mere 50 percent in a late June NBC/Wall Street Journal poll. It was enough to make one prominent White House reporter remark that, for the first time, he could envision the Bush presidency as a failure.

One person carefully attuned to the new president’s shifting fortunes is a man who clearly hopes to replace him four years from now: Massachusetts’s own junior senator, John Kerry. Kerry’s White House aspirations are no secret. He contemplated a challenge to Al Gore in 2000 but decided against it, reasoning in part that he’d waited too long to get his campaign airborne. So this time, he seems determined not to let his chance slip away.

Since roughly the moment Gore conceded the Florida recount, evidence of a Kerry candidacy has been visible everywhere–in his visits to Iowa and New Hampshire, his courtship of important advisors and activists, his noisy opposition to the new White House agenda, and the whispers of his political allies. Some other potential candidates, like 2000 vice presidential nominee Joe Lieberman, are waiting to see what Gore does. But by the look of it, Kerry is in.

He also happens to be a long shot. John Forbes Kerry is an impressive public figure. His life story includes both heroic service in, and noble protests against, the Vietnam War. He is surely one of the Senate’s most serious and intelligent members. Chris Matthews, the prosecutorial host of MSNBC’s Hardball, recently hailed Kerry for actually thinking about what he’s saying on television rather than just spitting out pre-packaged talking points.

But as a presidential candidate Kerry has as much going against him. It’s not just that US senators have such a dismal track record in presidential elections–not since John F. Kennedy in 1960 has one made it to the White House–or that the leg-up that Massachusetts politicians enjoy in the New Hampshire primary rarely translates into broad appeal in mainstream America. It’s also that many of Kerry’s potential rivals for the party nomination–Gore, Lieberman, House Minority Leader Richard Gephardt, and Senate Majority Leader Tom Daschle, for instance–start with higher name recognition, bigger national networks, and stronger natural constituencies.

As the field of candidates sorts itself out over the coming couple of years, Kerry will have to work doubly hard to get an edge on his rivals–hustling for media attention, attaching his name to popular issues, and making clear that he is deadly serious about winning. All of which will feed directly into the damning stereotype that has dogged Kerry throughout his career: that he is driven as much by personal ambition as by the larger principles of public service. It may not be fair, but it is a fact of Kerry’s political life. And it could pose a real problem as he heads down the unforgiving road to the White House.

Politicians who are driven by ambition are hardly an exotic species. But from the beginning of his career Kerry has been saddled with an unusually stark reputation for self-promotion. Perhaps it goes back to the revelation that the Vietnam medals Kerry threw over the White House fence in protest 30 years ago were not his own. Though Kerry angrily dismisses its significance, the tale has always served as foundation for what The Boston Globe described in 1996 as “nagging perceptions of him as insincere.”

Part of the problem is that, politically, Kerry has always been hard to define. He is neither the McGovernite liberal that Republicans would make him (and all Democrats from Massachusetts) out to be, nor a truly centrist New Democrat like Lieberman. But carving an independent course can also look like political calculation. For example, Kerry is now a member of the Senate’s New Democrat coalition, but he joined only last year, at a time when the group’s moderate patina had lost its element of political risk among the Democratic faithful; about one-third of Senate Democrats now belong to the group, including that liberal icon Hillary Clinton.

As a result, Kerry regularly finds himself the butt of unflattering insinuation. In 1998, Newsweek described Kerry as a member of the Senate’s “sanctimonious middle.” Last year, in the midst of his consideration as a vice-presidential choice, The New Republic, my full-time employer, slammed Kerry for a “long record of opportunism.” A CNN reporter recently noted that Kerry is often viewed as “a passionate advocate of himself.” And it’s not just Washington media elites who poke fun. When Kerry arrived late to an April dinner honoring US Rep. Joe Moakley shortly before he died of leukemia, former state Senate president William Bulger repeated a gibe he’s used against the US senator before, joking from the podium that “John Kerry got stuck in front of the mirror.”

Now that Kerry is considered an eager White House hopeful, the media treatment has only gotten harsher. In June, Howard Fineman’s Newsweek article about presidential ambitions in the Senate led off with some arch comments at Kerry’s expense. “Oceans and fisheries are riveting topics—-if you’re captain of a trawler fleet,” Fineman wrote. “If you’re running for president, you’d like to travel more widely. So when the Senate switched to Democratic control last week, Sen. John Kerry expanded the name of his subcommittee. Now it’s Oceans, Fisheries and the Environment. Global warming hearings start soon.”

Kerry’s name rarely appears in the media these days without a mention of his presumed ambitions. His early declaration that he would shut down the Senate with a filibuster, if necessary, to prevent Bush from winning approval of oil drilling in an Alaskan wildlife refuge was treated as something akin to a campaign stance. Meanwhile political junkies, who study television appearances like Kremlinologists, have taken note of a sudden surge in Kerry’s airtime. The Capitol Hill newspaper Roll Call, which has been keeping tabs on presidential aspirants, recently found that Kerry had notched more appearances on Washington’s Sunday talk shows this year (10 by mid-May) than any other Democratic member of Congress–and just one fewer than the intensely sought-after John McCain. And when Kerry does appear on television, he is nearly always confronted with questions about his 2004 intentions. As soon as Kerry finished denouncing the Bush agenda on ABC’s This Week in March, for instance, Sam Donaldson teased him for giving “a campaign speech…meant for the presidency in 2004.”

Kerry bristles at moments like these (“I can’t believe you guys are chasing 2004 already,” he snapped at Donaldson). And it’s easy to understand why. No one gets to be president without pursuing it single-mindedly, but wearing your ambition on your sleeve has its costs. In the 2000 campaign, Gore seemed to turn off voters with his unconcealed longing for the White House, retooling his image at every opportunity in a frantic drive to win. George W. Bush, on the other hand, managed to convey the sense that winning just wasn’t that important to him. Time and again, he made it clear that he could handle losing, casually acknowledging that “life would go on,” even as he scratched and clawed his way over McCain and then Gore.

But if Kerry comes off as a political free agent pursuing his own cause, it’s in part because, among Democratic constituencies, he’s no one’s natural favorite. Labor unions like Gephardt and Gore; the centrist Democratic establishment is partial to Lieberman; the media is hyping John Edwards, the telegenic young North Carolina senator; liberal interest groups will be inclined to reward Daschle for holding the line against Bush, and so on.

In the long run, being no constituency group’s golden boy could work in Kerry’s favor, but only if he presents a rationale for his candidacy that is bigger than himself. McCain attracted his following in part because of his epic personal story–but he held onto that following by connecting his story to an inspiring brand of patriotic reformism. Kerry will have to accomplish a similar feat–if he can weather the heckling.

CommonWealth Washington correspondent Michael Crowley is an associate editor at The New Republic.