Putting a thumb in the eye of Liberal Discontent, Part 2 (Party disunity actually helps)

Believe it or not. This from Erza Klein:

It was the primary challenge that drove Arlen Specter from the Republican Party that was ultimately responsible for health-care reform. Without Specter's temporary membership in the Democratic Party, Reid wouldn't have had the 60 votes needed for passage. Similarly, Joe Lieberman, who Democrats let hang onto his seniority even after he endorsed the Republican presidential candidate in 2008, was also a crucial vote for the health-care bill, though he certainly extracted his pound of flesh along the way. To put it another way, party disunity is probably responsible for Democrats' most important achievement in generations.

Republicans suffered for their unity this year, too. If not for primaries in which the much more conservative, but much less electable, candidate took the nomination, Delaware, Colorado and Nevada would've flipped to the Republicans. That would've left the Senate with a 50-50 split -- and made it much likelier that, say, Ben Nelson or Joe Lieberman walked across the aisle to hand control to the Republicans.

Party disunity isn't very emotionally satisfying. Quite the opposite, really. But it often works.