The now-common feature of Presidential nominating campaigns is frequent "debates" between the contenders. Of course, none of these are real "debates" at all, they are more like joint press conferences, but they do provide the opportunity to see the candidates side-by-side, answering the same or similar questions, for purposes of comparison. But do they really give the trailing candidates a chance to take down the frontrunner? The dynamics say "No," according to Steven Stark at Real Clear Politics:

Worse, the dynamics of the 2007 Democratic debates are destroying the campaigns of the major challengers. Take Edwards. His calling card is that he's the candidate of real change, and he's backed that up by taking stands on issues such as NAFTA, which separate him from the mainstream.

But every time Edwards goes to his left, Dennis Kucinich -- who has no chance to be president and therefore can take any stand he pleases with impunity -- goes further left. This has the effect of making Edwards look like just another timid moderate, which is hardly what he is.

If anything, Obama fares worse in these debates. His advantage is that he's different and new, with all the excitement that comes with those attributes. But the more he appears on a stage with seven very conventional politicians, the more he appears as conventional as they are. In every debate, he loses a bit more charisma.

Read the entire article at the link above. Stark has a point about the perception of negativity which attaches to debate criticisms. Challengers, however, almost have to criticize a strong frontrunner in some ways if they are to have any chance at all. Obama plays on Hillary's controversial image in his interview with the Washington Post:

But he also made a broader argument that more than a change in parties is needed to fix the country's problems. At one point, Obama said he was not singling out Clinton in saying that he is better able to pull the nation together than any of his challengers, but over the course of the 40-minute interview he volunteered a number of contrasts between his views and Clinton's.

"Her argument is going to be that 'I'm the experienced Washington hand,' and my argument is going to be that we need to change the ways of Washington," he said. "That's going to be a good choice for the American people."

The whole interview is at the preceding link. Edwards, too, is making note of Hillary's negatives, as ABC's Political Radar reports:

"I think the reality is people in this country either love Hillary Clinton or they don't. And that's just the way she is in many ways through no fault of her own. And I think that's what Obama was talking about," said Edwards in reference to an interview that Sen. Barack Obama, D-Ill., gave to The Washington Post.

While joining Obama in portraying Clinton as divisive, Edwards would not label her "corrupt" when prompted to do so by MSNBC's Chris Matthews.

Source at the link above.