Rod Dreher marvels at movement conservative enthusiasm for primary challenges in 2014:

This is astonishing, and can only be driven by an ideological mindset so impervious to reality that it would rather destroy political conservatism’s chances of actually running the country than succumb to the least impurity in the ranks.

The trouble here isn’t that incumbents are facing primary challengers, which can be a good and necessary thing, but that they are frequently facing challenges that seem to serve no purpose. The Cheney challenge to Enzi is the absurd extreme of this phenomenon: someone with a lifetime ACU rating of 92.7 has to head off a challenger whose sole reason for running is self-promotion. It is fairly harmless, but also completely useless. Challenging Alexander or Cochran might be more justifiable based on their voting records (their lifetime ACU ratings are 78 and 79 respectively), but even if successful they wouldn’t make it that much more likely that conservatives will be able to advance their agenda in Congress.

Cochran’s challenger has said, “I would have stood my ground and fought on the issue of defunding.” If McDaniel had been in the Senate to cast that vote, it wouldn’t have changed the outcome of the vote on the deal McConnell made, but it ought to make voters in Mississippi question his political judgment. “I would have stood and fought,” McDaniel says. Yes, and then he would have lost just as Cruz and his allies lost. If someone looks at the display Cruz put on in the last two months and concludes that he wants to support more of that, that should be counted as a strike against him.

A more practical problem with bad primary challenges is that they waste limited resources that could be put to more productive use ousting Democratic incumbents or winning open seats. There is no danger that the Democrats will take advantage of intra-Republican feuding in many of these states, but much of the time, effort, and money spent on unseating Cochran or Alexander won’t be spent on defeating the Democrats that stand in the way of Republican control of the Senate. There’s nothing wrong with challenging incumbents from your own party, but there have to be good reasons to do it that go beyond a desire for increased combativeness for its own sake.