I’m sympathetic to the case that Ezra Klein and Matthew Yglesias (among others) have been making against the institutionalization of the filibuster in the Senate, but the debate has often felt highly abstract. Other than a brief spate of posts on whether the filibuster helped block President Bush’s Social Security legislation in 2005, advocates of reform have rarely grappled with how legislative outcomes might change in a filibuster-free Senate.

To make things more tangible, I’ve created the following table listing the pivotal voters for proposals moving policy toward the president under majority rule and the filibuster*:

Looking at these names, it’s clear that a switch to majority rule would have had a substantively important effect on the ability of the president and his party to enact legislation (with the possible exception of the 110th Congress in which the Democratic House was the key check on President Bush). Under the gridlock zone model of Congress, the filibuter pivot is the key constraint on the president’s legislative agenda (unless the median voter in the House is further away from the president).

To illustrate the point, I constructed a table of key votes selected by Americans for Democratic Action that attracted majority support but failed to reach the 60-vote threshold for cloture:

In addition, many other policies would likely have passed the Senate in substantially different form (i.e. more conservative in 2001-2006, more liberal in 2007-2009).

In the end, the institutionalized filibuster adds yet another veto point to a system that already has too many, which weakens the democratic responsiveness of American government. But there’s a very real tradeoff — the price of responsiveness is responsiveness to ideas you don’t like when your party is out of power. There’s no getting around that fact.

* Rankings drawn from the Lewis-Poole Optimal Classification scores for the 107th-111th Senate. I assume the proposal in question would move the status quo toward the president, so the pivotal voter under majority rule would be the 50th most conservative (under Bush) or most liberal (under Obama) since the vice president would break the tie in favor of the president. Similarly, the filibuster pivots are the 41st most liberal (under Bush) or 41st most conservative (under Obama). I adjusted the 111th Senate rankings to account for the replacement of Ted Kennedy with Paul Kirk (who I assume is more liberal than Hagan and Nelson) but otherwise didn’t account for special elections and appointments.

Update 12/9 4:25 PM: Matthew Yglesias argues that “the three progressive initiatives that were blocked by the filibuster [in the table above]—higher minimum wage, Iraq withdrawal deadline, and timely economic stimulus—are considerably more significant than the conservative initiatives that were blocked.”

That may be true, but two other factors are worth considering. First, as I noted above, the filibuster prevented more extreme versions of major conservative proposals such as the 2001 and 2003 tax cuts (correction: passed under reconciliation). Second, and perhaps more importantly, there are presumably a number of other bills in 2001-2006 that might have attracted fifty votes but were never brought to the floor because they couldn’t reach the threshold for cloture. If it’s clear that a bill can’t pass, it’s likely not to be considered. Conversely, the list above is skewed toward nominees (who can’t be amended to mollify the filibuster pivot) and high-salience issues (on which senators are more likely to want a recorded vote even if it fails).