Why the filibuster is OK for Democrats but not for Republicans.

The unraveling of the congressional debate over health care reform is already renewing calls to abolish the Senate filibuster. As many have argued, the filibuster undermines the democratic principle of majority rule and compounds the unrepresentative character of the Senate's design. The health care debacle suggests that the filibuster may also be rendering our country ungovernable. So why not just do away with it?

Because one of the most entrenched assumptions about the filibuster—that it thwarts majority rule—is only half-true. When you crunch the numbers, it turns out that the filibuster has often served to enforce majority rule in recent years, not to undermine it. Instead of abolishing the filibuster, we should try to curb its undemocratic excesses while preserving its role as a democratic check.

Of course, the filibuster is by definition a tool for a Senate minority to obstruct a Senate majority. But since Rhode Island and California enjoy equal representation in the Senate, a majority of senators isn't the same as a majority of Americans. To gauge the relationship between the filibuster and national majority rule—the kind where everybody counts equally, and the representatives of the majority carry the day—it's necessary to look at the data.

To do this, I downloaded records of all Senate votes on cloture motions—used to limit debate—from 1991 to 2008. For each of the 152 votes where a filibuster successfully thwarted a Senate majority, I tallied the populations represented by the senators who supported the filibuster. (A more technical explanation—including some significant details I've glossed over—is available here.)

What do these calculations reveal? First, over the past two decades or so, the senators who successfully filibustered something represented about 46 percent of Americans on average. Yes, that is a minority—but it is a far cry from the nightmare scenarios sometimes deployed by opponents of the filibuster, who worry that as little as 11 percent or 12 percent of the country could obstruct popular legislation. Since 1991, in fact, there have been only four filibusters—0.03 percent of the total—that thwarted senators representing more than 65 percent of the American people.

What's most striking, though, are the many cases in which the filibustering Senate minority has actually represented a majority of Americans. In fact, in 40 percent of the filibusters since 1991, the senators making up the "obstructionist" minority represented more people than the majority they defeated.

The traditional debate over the filibuster—which equates filibustering with a minority veto, and then argues the merits of giving the minority such a prerogative—entirely misses this fact. Democratic filibusters against President Bush's judicial nominees were decried as undemocratic usurpations, for example. But nearly all of them fell into this category of "majority rule filibusters."

This example is typical of a more general partisan pattern. When Republicans have been in the majority, the filibustering minority has actually represented the majority of Americans 64 percent of the time. When Democrats have been in the majority, that figure plummets to 3 percent. So the charge that it is somehow hypocritical for Democrats to decry Republican filibusters as affronts to majority rule—if they also stand by their past decisions to filibuster the Republicans—is easily answered. When Democrats have filibustered Republicans in recent years, they have very often represented more Americans than the Republican majority; the same is almost never true in reverse.

All of this suggests that reformers should not be too quick to reject the filibuster outright as an impediment to democracy. During recent periods of Republican control, the filibuster has served as a democratic backstop that counteracts the structural inequality of the Senate—often empowering a majority of Americans, acting through their senators, to veto extremist bills or nominees.