Jonathan Martin and Mike Allen report:

Former Massachusetts governor Mitt Romney accused Democrats of cowardice in ducking presidential debates hosted by sponsors they dislike, saying that Republicans have proven more willing to appear in potentially hostile forums.

Romney said the May 3 debate at the Ronald Reagan Presidential Library -- co-sponsored by The Politico and MSNBC -- proves that Republicans "have a lot more courage of our convictions," because they are willing to take questions from a moderator who earlier in his career worked as an aide to Democratic politicians. Democratic presidential candidates have refused to take part in two debates co-sponsored by Fox News, arguing that the network is slanted toward Republicans.

"Why is it that the Democrats wouldn't even go on Fox, but we Republicans are happy to sit there and have Chris Matthews of the Carter administration, former chief of staff to (ex-House speaker) Tip O'Neill?" asked Romney, in a Tuesday evening interview here with The Politico. "We're happy to sit there and have him dish questions to us, but they won't even go on Fox."

Why other Republican candidates didn't jump on this angle right away is beyond me, because in addition to being obvious and true, it plays well with the base on a number of levels. The idea that Brit Hume is somehow more partisan or less professional than Chris Matthews, Tim Russert or George Stephanopoulos is beyond laughable.