We may see a record number of congressional incumbents lose their primaries this year. If we do, it’s likely to have more to do with redistricting than a wave of so-called “anti-incumbent” sentiment.

Rep. Silvestre Reyes (D-Tex.) was chairman of the House Permanent Select Committee on Intelligence until 2011. He lost his primary Tuesday. (Kevin Clark/The Washington Post)

With Rep. Silvestre Reyes’s (D-Tex.) loss Tuesday, we are now guaranteed to see 15 incumbents lose primaries in this post-redistricting cycle. Four have lost to non-incumbent challengers, and 11 more face or have faced primary matchups with other incumbents, assuring that one incumbent will fall.

So if five additional incumbents fall to primary challengers, 2012 will tie the record of 20. And there are LOTS of primaries yet to come. (We should note that it used to be more common for incumbents to lose primaries, but getting data for elections going back more than 50 years is difficult at best.)

But those totals don’t really tell the whole story.

While 2012 may wind up equaling 1992 for incumbent losses, 1992 was actually much more unkind to incumbents. That’s because the vast majority of incumbents who lost that year (17 of the 20) fell to challengers rather than other incumbents.

Indeed, 2012 is unusual for the number of incumbent-versus-incumbent primary matchups (and the lack of such matchups in the general election), which will inflate the number of incumbents who wind up losing primaries. So unless many more incumbents start losing to challengers, it’s hard to compare it to 1992, because so many of the incumbent losses this cycle were preordained.

That’s not to say that 2012 hasn’t been (relatively) unkind to incumbents. It’s rare to see even four incumbents lose in primaries, and many other incumbents — including Rep. Ralph M. Hall (R-Tex.) on Tuesday — have been held below 60 percent of the vote.

But much of that has to do with redistricting. Indeed, at least two of the four incumbents who have lost to challengers — Reps. Jean Schmidt (R-Ohio) and Tim Holden (D-Pa.) — saw their districts undergo significant changes.

Reyes and Sen. Richard Lugar (R-Ind.), meanwhile, both had significant vulnerabilities — Lugar with his steadfast nose-thumbing at the tea party and residency issues and Reyes with multiple ethics complaints.

In other words, whatever anti-incumbent sentiment is out there, it’s wholly insufficient for taking down an incumbent in a primary; it needs help from either the incumbent falling asleep on the job or a friendly draw from redistricting.

And those sets of circumstances are still very much the exception rather than the rule.