Sen. Lindsey Graham's (R-S.C.) relatively easy primary win last week was hailed by immigration reform activists as a counterpoint to House Majority Leader Eric Cantor's (R-Va.) loss to a tea party challenger.
Cantor's loss couldn't have been all about immigration, they argued, because one of Congress's top immigration reform advocates (Graham) won so easily on the same exact day.
What that analysis misses, though, is that Graham's share of the vote — 56 percent — was extremely low for an incumbent. In fact, since 2004, only 4 percent of congressional incumbents running for reelection have been held under 60 percent of the vote in their primaries.
In other words, Graham won a clear victory, but he also clearly alienated a significant portion of GOP primary voters and faced a somewhat scary primary because of it.
Graham's showing is actually quite notable, because it's one of an increasing number of semi-competitive races for incumbents. We wouldn't necessarily call them all "close calls" (especially since Graham won by 40 points against a scattered field of opponents), but being in the 50s isn't exactly comforting for an incumbent — especially when you consider that many who drop below 60 percent in one election wind up losing their primary in a later election.
Prior to Cantor's loss and Sen. Thad Cochran (R-Miss.) falling into a runoff this month, there was plenty of talk about the lack of incumbents being beaten by the tea party. And there is something to that, as the percentage of incumbents losing primaries is still lower than in either the 2010 or 2012 elections.
But if you look at the bigger picture, you will notice that the number of incumbents getting at least a little scare has gradually increased over the years. And it's actually higher this year than in any recent election.
While in 2004, fewer than 3 percent of incumbents fell below the 60 percent threshold in their primaries, so far in the 2014 election it's more than 5 percent. The number of incumbents under 60 percent is also up significantly from 2012, when it was 4.3 percent. In 2010, it was 4.9 percent.
(Note: These data include only party primaries and not nonpartisan primaries in states like California and Washington state -- in which many candidates fall below 60 percent because all candidates run in the same primary.)
A big reason why there have been fewer incumbents upset is that the GOP establishment has gotten better at dealing with the tea party. Indeed, only about half of the 12 incumbents falling below 60 percent were Republicans facing tea party challengers.
But there are also so few instances of competitive primaries (generally between 12 and 20 a cycle) in which a lot of this is circumstantial. Candidates, money and other intangibles matter, and sometimes it's enough to oust an incumbent. Most of the time it's not.
And given the increasing number of competitive primaries, it was only a matter of time before something like Cantor or Cochran happened.