Lots of events in politics are overhyped and are deservedly forgotten weeks, or even days, after they happen. The defeat of a sitting U.S. senator in a primary election isn’t one of those events. The primary last night in Mississippi, and the likely victory of Chris McDaniel over incumbent Senator Thad Cochran in a runoff, certainly do matter.

First, the Senate is a small place, and every lawmaker is important. Even if Senator McDaniel voted almost identically to how Cochran would have voted, he still could do plenty that would make a difference.

Then there’s the demonstration effect for future insurgents. Even in the very unlikely event that McDaniel lost the general, the primary win he scored for the Tea Party will make the next one a little easier. In the long run, that means more radical Republicans in the Senate and, most likely, a few more Democrats.

But those most affected will be incumbent mainstream conservative senators. Politicians learn from example. And there’s nothing more seemingly obvious than the difference between the incumbents who have lost recent primaries and those who survived high-profile challenges. Bob Bennett, Dick Lugar, and Cochran all lost (assuming the runoff goes as expected) after running safe, conventional campaigns. That contrasts with the aggressive and successful efforts of John McCain, Orrin Hatch, and Mitch McConnell to channel the Tea Party to secure renomination.

It’s nice for the radicals to add one more of their own to the Senate. But it’s a much bigger deal to get two-thirds or so of the mainstream conservatives trying hard to imitate the radicals. That’s been going on for the last few years, in the House and Senate. The Mississippi primary is going to make it even more common.

[Cross-posted at Bloomberg View]

Jonathan Bernstein

Jonathan Bernstein is a political scientist who writes about American politics, especially the presidency, Congress, parties, and elections.