I don't think they can, but it would be stupid to do so. As it is, the Democrats have a 51-to-49 majority in the Senate. That means that they are in control of ... well, without getting too far into it, everything in the Senate. If they were to get rid of him, they would no longer have control. Also, on most issues that are more core but less glitzy, he does tend to vote with the party. It's just that he's in favor of the Iraq war and, in relation to this thread, video game censorship, although another big proponent of that is Hillary Clinton, and few would call her a DINO.