Who made the biggest welfare cuts in my life? Clinton. Who enacted the biggest welfare increase since LBJ? Bush II. In domestic and foreign policy, Bill Clinton was a far more conservative president than Dubya has been, in total defiance of their labeling.
The dynamics behind these facts are not hard to discern. What's really important in American politics is that the people on top stay on top. What you couldn't do and get elected is, say, promise to cut defense spending by 50%, or make copyrights die with the creator of a work. Disney and Halliburton would unite to see you crushed, and suddenly there'd be lots of stories in the press about how you seem somewhat "unstable," a bit of a "nutjob" -- think Howard Dean. On the issues that don't matter much to the elite, say, prayer in schools, you can play to the base and draw out sharp differences. But once in office, there's no gain to be had from doing much about it -- instead of your radical program, you wind up tweaking the status quo at the margins, maybe even moving towards your opponent's position. E.g., how much alteration in the abortion situation has happened since Roe vs. Wade, despite multiple Republican presidents and congresses? Somehow, once in office, they just can't quite seem to get around to doing much about an issue they were all fired up about when they were speaking to that BBQ crowd in Utah! Just like the Dems, once in office this year, didn't see any real reason to make a fuss about Iraq or eavesdropping. They know the people who believe their marketing, i.e., that they're the "progressive, caring" party, have nowhere else to go. And if Democrats lose control of Congress? Well, it's off to a nice lobbying jobs! The important thing is, once you're "in," don't rock the boat.
This all would have been quite obvious to Marx. But it's kind of hard to admit you're being played for a fool.