Republican chances for a Senate majority in 2015 took a bit of a hit today, with senior GOP Rep. Dave Camp announcing that he won’t run for the Michigan open seat. Whatever Camp’s chances, he was the GOP’s top choice, and with him out the chances are extremely good that Democrats will retain this seat.

This points to a broader, if mostly hidden, risk that the radicalization of the GOP primary electorate and many of its party actors poses for the party’s long term hopes.

Everyone talks about Senate seats lost to Republicans by awful candidates foisted on the GOP by the Tea Party, such as Todd Akin and Christine O’Donnell. But perhaps even more important is another Tea Party effect: the prospect of Tea Party upsets convincing strong candidates that primary elections are a hurdle they can’t surmount — leading them to decide not to run.

Candidates are important in Senate elections — it’s often the case that a strong candidate can be the difference between a sharply contested race and one that fizzles. The best candidates are usually professional politicians, and those politicians are, in the lingo of political scientists, strategic: they choose to run only when they believe that it’s a good time to run. It’s always a bit tough, then, to get them to take on an incumbent, or to run in a state that leans towards the other party. But the possibility of Tea Party upsets in primaries make it that much more difficult. If Senators Bob Bennett and Richard Lugar can’t get renominated, then why should someone such as Camp risk it when he has a perfectly safe House seat that he would have to give up?

We don’t get to know exactly how much of a factor this is in any particular decision. But there are signs it could broadly matter. In the last cycle, Republicans failed to recruit a solid challenger in states such as Florida, Ohio, Pennsylvania, and Michigan — all states in which Republicans have at least a fighting chance. That seems to be happening this time around in the campaigns for open seats in Michigan and Iowa, and in the races against potentially vulnerable Democrats in Minnesota, Colorado, New Hampshire, and perhaps two or three others.

Of course, all parties have recruiting failures. Democrats are striking out so far in open seats in South Dakota and Montana. But overall, it’s the GOP that has had the most recruiting trouble lately, and it’s almost certainly because Republican leaders can’t be trusted to clear the field for strong candidates. The temptation to support insurgents, even ones who would badly hurt the party’s chances in November, is just too strong for both party actors and voters in Republican primaries.

It’s a real, and underappreciated, cost of the Tea Party effect. And it’s not going away any time soon.