THE PERILS OF BIPARTISANSHIP IN A LOPSIDED CHAMBER…. Matt Yglesias raises a good point about a legislative dynamic that often goes overlooked: trying to govern in a bipartisan fashion is tricky when the minority keeps shrinking.

Say, for example, the Senate passes an important piece of legislation with 62 votes. Ordinarily, that would point to a healthy, bipartisan majority. Except, of course, given the current makeup of the Senate, it suggests the bill passed with literally only a couple of votes from the minority. That’s what happens when the Republican caucus goes from 55 to 49 to 41 to 40 over the course of a few years.

[A] big part of the story is that Republicans who held vulnerable seats nonetheless voted in lockstep with their party leadership’s conservative agenda. Democrats, by the same token, got to where they are because the caucus tolerates many members who frequently deviate from the party line. But this means that the GOP has managed to make itself small precisely by minimizing the number of people who are likely to cross party lines.

On Inauguration Day, there were only three Republicans left who regularly joined bipartisan compromises. Obama got all three for [the stimulus package]. And for his trouble, Senator Specter got essentially booted from the party. So now there are really only two “gettable” Republicans left. So does an Obama bill that Collins and Snowe sign on to [count as] a “bipartisan” bill?

When it comes to major legislation, there are very few bills that are going to garner 90 or more votes. The practical definition of a bipartisan bill is one that enjoys the near-unanimous support of one party, while peeling off the moderates of the other. In 2009, however, there are only two Republican moderates left. Somehow, though, a 62-vote majority for a bill is perceived as a “failure of bipartisanship.”

Let’s not lose sight of how we got to this point. One party, which was in the majority not too terribly long ago, effectively discredited itself with bad ideas, failed policies, and incompetent governing. Voters decided they wanted fewer members of this party making policy decisions at the federal level.

For the David Broders of the world, who prioritize bipartisanship above all else, it creates an untenable dynamic. A failed, shrinking party, with precious few moderates, doesn’t like the majority party’s agenda. That’s fine; that’s what opposition parties are for. At the same time, however, the majority party is supposed to pass legislation that enjoys the support of the failed, shrinking party — because it “looks” better.

I continue to think this places the burden in all the wrong places. It’s not Democrats’ fault that voters have rejected Republicans in large numbers, leaving the GOP with only a couple of moderates. “Bipartisanship” will be more common when the Republican Party moves closer to the American mainstream, not when Dems water down important legislation.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.