The gloves will come off, Barack Obama has promised his supporters, and it looks like he may have already taken his first swing at negative politicking. Calling Hillary Clinton one of the most secretive politicians in America, the Obama campaign publicly demanded that Hillary release her tax returns. Team Hillary responded with a Rezko question:

Barack Obama’s campaign took fresh aim at Hillary Clinton Wednesday for refusing to release her tax returns, asking in a memo circulated to reporters, “What does Clinton have to hide?”

“In the face of her unwillingness to release her tax returns, Hillary Clinton has made the false case in this campaign that she is more electable because she has been fully vetted,” the memo stated. “When it comes to her personal finances, Senator Clinton’s refusal to release her taxes returns denies the media and the American people the opportunity to even begin that process.”

David Axelrod, the Obama campaign’s chief strategist, also said in a conference call with reporters Wednesday that Clinton has a history of non-disclosure and is the least-vetted candidate in the presidential race.

Clinton had said she will only release her tax returns if she captures the Democratic nomination, though her communications director, Howard Wolfson, issued a statement Wednesday indicating she would do so around April 15.

The demand also came from Obama himself, an interesting development. Obama had insisted that he would not get into attack politics, and for a while he didn’t need to do so. Until Tuesday, Obama had rolled up eleven straight victories in primary contests and could afford to keep himself above the fray.

Unfortunately, that left him vulnerable to Hillary at just the moment when two obstacles appeared in his path to the nomination: the NAFTA Dance and Tony Rezko. Hillary exploited both openings, and Obama’s response hardly gave an indication that he could fight a tough general-election campaign. Now he has to answer Hillary’s attacks with some of his own, not so much to increase her negatives — could they go any higher? — but to prove to the superdelegates that he is up to the task in the general election. A few more stumbles and his pledged delegate lead may not be relevant in Denver.

The question then becomes whether Obama can maintain the image of a reformer and a new kind of politician while personally engaging in negative campaigning. For people like John McCain or even Hillary, their resumes give them a clear identity. Without his identity as the savior of modern politics, Obama has almost literally nothing to present to voters.

UPDATE: Is it wise for Hillary Clinton to bring up Ken Starr?

Clinton communications director Howard Wolfson just said on a conference call with reporters: “I for one do not find that imitating Ken Starr is a way to win a Democratic primary election for president.”

So asking for tax returns somehow equates to a supposed witch hunt about sex?  What did Hillary do to earn money, anyway?