by Michael Olson and Nancy Cook

The McCain camp has released a new ad — on the eve of the Democratic National Convention — questioning why Obama didn't ask New York Sen. Hillary Clinton to be his running mate. Titled "Passed Over," the ad says that Clinton was dropped as a possible VP candidate because she "spoke the truth" about Obama's plans and attacks, calling them vague and negative. As NPR's Nancy Solomon reported in June, McCain has been wooing ex-Clinton supporters since Clinton left the race.

"Passed Over" takes a similar approach to McCain's ad from yesterday featuring Biden. Both ads use clips of former Obama challengers (now supporters) to emphasis the McCain camp messages that Obama is inexperienced.

UPDATE: Clinton's Spokeswoman Kathleen Strand provided the following response hours after the McCain camp released "Passed Over":

"Hillary Clinton's support of Barack Obama is clear. She has said repeatedly that Barack Obama and she share a commitment to changing the direction of the country, getting us out of Iraq, and expanding access to health care. John McCain doesn't. It's interesting how those remarks didn't make it into his ad."