Personally, I'm not to concerned about that number because it's March.
As for an explanation of the number, I think TPM reader AK gets it right,
Forgive me if I missed you saying this on your site, but there's any easier way than a structural argument to understand why many Clinton supporters say they'll vote for McCain instead of Obama: Clinton, whom they support, and, one assumes, trust, has told them to do so. She has made the case that the pecking order, particularly when it comes to [Commander-in-Chief], is her, then McCain, and Obama failing the threshold test. She has said the same about judgment and experience. This is a case where considering a structural -- to use your word -- double move is too clever by half. All you need to do is look at what they're being told by the Clinton camp to understand the polling numbers.And it's unforgivable. The Clintons frequent flattery of John McCain is just bizarre. When was the last time a republican had anything nice to say about their democratic opponent? And it's both the Clintons who flatter McCain almost every day.
Some suggest Hillary is already looking to 2012 if she's not the nominee this round. Crush Obama so that if he gets the nomination, he losses the general, and come back in 2012 on the "I told you so" campaign. , with McCain then would be 76 and America having had 4 years to soak up just what '100 happy years' in Iraq really means. I'm not that cynical.