McCain sort of promised Harry Reid and other Dem leaders that he would vote with Dem caucus if he wins. This saves him from their withering fire. But if they start to push him around, he can always switch. He could switch anyway, but would be seen as a turncoat (ala Jumping Jim Jeffords). He might also incur the wrath of Connecticut voters, but he will probably not want to run again anyway. Next to Zell Miller, Smokin' Joe is my favorite "Dem" Senator.
What more would anyone need to know about McCain?