Democratic presidential hopeful Sen. Barack Obama, goes after Sen. Hillary Rodham Clinton for her stand on health care during the Nov. 15 debate. (AP Photo/Jae C. Hong)

Offense is defense, and defense is offense. – Unattributed judo quote

Two months ago, I didn't know anyone who thought Hillary Clinton would lose. Today, I don't know anyone who thinks that she'll win. Such is the seismic shift the past few weeks have seen in the conventional wisdom of DC's chattering class. Barack Obama's quiet creep to the top of the polls in Iowa had already set people talking.

But then came Hillary Clinton's ham-handed attacks on his kindergarten essays about the presidency. And then came Oprah, and her thousands of potential new Obama caucus-goers. And then came the repugnant comments of Bill Shaheen, who stepped down yesterday from his post as co-chair of Clinton's New Hampshire campaign; he suggested that Obama's youthful drug experimentation might lead wise voters to think twice about the untested Senator from Illinois. And suddenly it looked like the Clinton campaign was flailing -- buffeted by bad press and bad decisions at precisely the instant that the Obama campaign could do no wrong.

Indeed, Shaheen's smears are being touted as the game-changer -- the potential Dean Scream for the Clinton campaign. But they're only the most media friendly example of what's changed in the race: What separates this month from last month is that the "politics of hope" have stopped working against Obama, and started working for him.

Back in October, the New Republic's Michael Crowley sought to assess why the Obama campaign seemed so sluggish. He quoted a rival campaign aide saying, "Clinton's baiting Obama into a unilateral nonaggression pact was maybe the single most race-changing event we've seen." The aide was right. Until that point, Obama had seemed almost allergic to aggressive campaigning. Every time he even dipped a toe into choppier waters, the Clinton campaign taunted Obama with his own rhetoric, asking him, "what happened to the politics of hope?" It was devastating. Obama had let them define his campaign's central theme: The politics of hope, it turned out, meant that you couldn't attack Hillary Clinton. For Clinton, that was a very hopeful development.

Obama wasn't the only candidate in the race, though. November might have seemed like a sleepy interregnum, but Edwards spent most of it assaulting Clinton in Iowa, attacking everything from her corporate ties to her husband's record to her "doublespeak." The press also turned on the frontrunner, assailing her over the issue of driver's licenses for illegal immigrants, then helping to mutate it into a question of forthrightness, and then turning that into endless speculation over whether she was playing the gender card.

And so Clinton's numbers slowly slipped. By the November's end, Obama was routinely leading in the polls. The Clinton campaign, noticing this, did exactly what you're supposed to do when you're a couple points behind: They tried to knock the other guy down. And ended up on the floor themselves. Obama, it turned out, had spent so much time inveighing against political attacks, and the Clinton campaign had invested so much energy in popularizing that sentiment, that their every assault now began to backfire.

A press release meant to dramatize Obama's long-standing ambition for the presidency and disprove his assertion that "I have not been planning to run for president for however number of years" got them in trouble for dredging up his kindergarten essays to use in an oppo document. Even for politics, that was a bit classless. Then came an e-mail attempting to direct attention to the fact that, 11 years ago, Barack Obama offered some inconveniently liberal answers on a candidate questionnaire. The e-mail exactly mimicked a similar dispatch from the Republican National Committee, which isn't the sort of resonance that warms liberal hearts. Then Clinton's campaign sought to accuse Barack Obama of operating a slush fund. Then Shaheen brought up his youthful drug use -- a particularly charged and ugly line of attack, given Obama's race.

In theory, any of these assaults could've been devastating to the Obama campaign. But for lack of a better metaphor, Obama had rendered himself rubber, and made Clinton into glue. The two of them had so strongly defined the "politics of hope" as an admonition against negative campaigning that any serious attacks against the other rebounded to the attacker's detriment. Obama, to his credit, rapidly grasped this new reality. Rather than strike back, he simply dramatized the fact that Clinton was striking at all. He created a Web site called "Hillary Attacks" which simply collects the examples of her campaign's charges. It doesn't seek to fact check them, or rebut them, it simply gathers them in one place, so voters and journalists can see how forcefully negative the Clinton campaign has become.

It's become a campaign that rewards only counterattacks, never attacks, and thus a campaign that almost uniquely advantages whoever leads in the Iowa polls. Any attack instantly spins into a meta-commentary on the attacker, proving them someone who engages in tawdry, dispiriting, "old politics." In this campaign, the best offense is proving to be a good defense. And the worst offense is proving to be any at all.