[T]he survey found that Mr. Obama, whose lead in the race for the delegates needed to secure the nomination has given him a commanding position over Senator Hillary Rodham Clinton since February, is now perceived to be in a much tighter fight. Fifty-one percent of Democratic voters say they expect Mr. Obama to win their party’s nomination, down from 69 percent a month ago. Forty-eight percent of Democrats say Mr. Obama is the candidate with the best chance of beating Senator John McCain, the presumptive Republican nominee, down from 56 percent a month ago.
Mr. Obama still holds an edge over Mrs. Clinton on several key measures; for example, 46 percent of the Democratic primary voters say he remains their choice for the nomination, while 38 percent preferred Mrs. Clinton, who has lost support among men in recent weeks. On that question, his margin actually grew, to eight from three points, over the past month.
Mr. Obama also has an advantage over Mrs. Clinton in ratings on honesty and integrity, in sharing the values of most Americans and in being less beholden to special interest groups. [Emphasis added.]
I would say that the percent of Democrats who support Obama versus Clinton is the key measure, and it is trending in Obama's favor in this poll. The only "damage" that has been done to Obama is that fewer Democrats think he will become the nominee, even though the same percentage still supports him. That's a pretty interesting media effect -- the plurality of Democrats still back him, but they (incorrectly) assume that others are no longer doing so.
*I recognize that I am linking to a Sides post that links to me. Please pardon the circle jerk.