Marc Ambinder makes a useful comparison between the Tea Partiers and the Netroots:
The Tea Party movement has been very successful in finding and running candidates for Senate because of the political economy of scale. But the gap between the threshold level of acceptability between the party and its activist base is wider than the gap between Democrats and the Netroots ever was. Even as Harry Reid has had to herd cats at times, as many headaches as Democrats have developed from having to deal with an internal affairs force within the party, it will pale in comparison to what Republicans will face in power if they try to adhere to their current norms.
The people who made things hard for the Democratic leadership are the centrists, who abandon them on tough votes and do a lot to undermine the messages they want to send (as some did on health care, and are doing right now by coming out in favor of extending the Bush tax cuts for the wealthy). But there's no real comparison with the Republicans, because they have so few moderates left. So will their extreme right-wingers make things difficult for them?
I think the answer is, only occasionally, and only symbolically. When it comes to votes, the Tea Partiers who make it to Congress will be on the same side as the GOP leadership. Centrists can side with the other party, but what is Congressman T. Party going to do if he thinks what Speaker Boehner is pushing isn't conservative enough? He might say some crazy stuff that Keith Olbermann will mock, but he won't be sabotaging his party's agenda, because there'll be nowhere for him to go. This is the quandary progressive members often find themselves in -- they can threaten to bolt over something like the public option, but everyone knows that at the end of the day, they won't turn their back on progressive goals, even if the legislation isn't all they want.
That isn't to say that the extremists who get elected in the fall (and regardless of who ends up in control of the House, there will be at least a few of them) won't be making noise. But in the end, there's only so much damage they can do to the GOP.
-- Paul Waldman