McCain was for it before he was against it:
John McCain… on a Wednesday morning campaign flight, told The Weekly Standard he’d consider a pro-choice running mate to share his ticket this fall. Which is odd, because just four months ago, he told Chris Matthews that it would be “difficult” to choose someone who is pro-choice. Which itself is odd because the last time he ran, McCain made clear that if nominated, he would indeed consider a pro-choice candidate. Which in turn is odd because for twenty years before that, McCain held a nearly perfect anti-choice voting record and firmly held anti-choice views.
McCain’s pretty good at telling a given audience what they want to hear (noble exception: ethanol subsidies). So he ends up fliping back and forth on certain things, especially domestic and cultural issues that he doesn’t seem to care about. When he gets caught in a contradiction, he makes a joke! That’s worked pretty well so far, I wonder if it will ever come back to bite him.