Death spiral

Arlen Specter switches parties, giving the democrats a good chance of achieving a filibuster-proof majority in the senate, and Rush Limbaugh's reaction was to suggest Specter take John McCain with him. The Republicans appear to be a party in free fall. Nate Silver of Fivethirtyeight gave a reasonable explanation for what's happening to the Grand Old Party:

Thus the Republicans [...] are in something of a death spiral. The more conservative [...] their message becomes, the more they alienate non-base Republicans. But the more they alienate non-base Republicans, the fewer of them are left to worry about appeasing. Thus, their message becomes continually more appealing to the base -- but more conservative, partisan, and strident to the rest of us. And the process loops back upon itself.

The partisan in me cheers, and the prospect of democrats controlling the 60 senate seats needed to reform health-care and to do something about global-warming (though it's still a long-shot) should make any liberal feel hopeful. But, while I don't think the Republican party will ever disappear entirely, a small, ideologically rigid right-wing party isn't necessarily a good thing for anyone, even if that party won't win elections.

Party systems work well for a few reasons. A opposition party can serve as a vehicle to punish the misdeeds of the ruling party. In Canada, people were angry at the long ruling Liberals after the "sponsorship scandal," so they gave the Conservatives a minority government. Then, the Liberals picked a feckless leader and Canadians gave the Conservatives a slightly larger minority during the last election. The Conservatives in turn, misinterpreted the nature of their mandate, and now they're down in the polls while the Liberals are up. In the American case, much of the outcome of the last election can be seen as Americans punishing Republican misrule and incompetence. For this purpose, it doesn't really matter who or how big the opposition party is, as long as they have the resources to challenge the ruling party at every level.

The other big reason 2 or more viable parties help a political system work is competition. Just as free-markets are efficient and dynamic because of competition, political parties compete at the market place of ideas, and everyone benefits. But here it does matter who the parties are. If the Republicans turn inward and spend all their energy pandering to an irrationally angry base, then they aren't seriously competing, and Democrats will become complacent and eventually stagnate.

After 8 years of Republican misrule, it is hard to not enjoy watching that party fall apart. But we should be hoping that they moderate, and put themselves back together.