Debbie Lesko nearly lost a district no one thought a Republican could ever lose. So her first move is to join the House Freedom Caucus? Photo: Matt York/AP/REX/Shutterstock

One of the underpinnings of our entire political system is the notion that political competition keeps elected officials from embracing extremism. It’s encapsulated in a social science “rule” dubbed the median voter theorem, which Tyler Cowen described neatly a few years ago:

[T]here is a dynamic that pushes politicians to embrace the preferences of the typical or “median” voter, who sits squarely in the middle of public opinion. A significant move to either the left or the right would open the door for a rival to take a more moderate stance, win the next election and change the agenda. Politicians will respond to this dynamic, whether they are power-seeking demagogues or more benevolent types who use elected office to help the world.

So it should raise a few eyebrows today that the newest member of Congress, Debbie Lasko of Arizona, fresh from a spare five-point win in a special election, is expected to make her first move in Washington by joining the proudly obstructionist right-wing House Freedom Caucus, according to HFC chairman Mark Meadows.

This actually requires a formal invitation after a formal vote by the HFC membership; that’s how selectively radical the group has become. But Lesko is expected to fit right in, says Meadows.

Now it’s true that Meadows and another key HFC member, Jim Jordan, endorsed Lesko in a tough multi-candidate primary; the pressure to Go Hard Right was intense, since one opponent, Steve Montenegro (fatally damaged in the end by a sexting scandal) was being backed by Joe Arpaio, who is wildly popular among Arizona’s eighth-district conservatives, and Ted Cruz. But Lesko also had strong general election backing from a House Republican leadership that generally regards the HFC as an existential challenge to their future.

Perhaps Lesko is aligning with these ideologues out of pure conviction: She is best known for sponsoring radical school-voucher legislation that if fully implemented (it faces a ballot initiative this November that would veto it) would all but destroy public education in her state.

But still, it’s remarkable that someone who nearly lost an un-losable district would think her first political priority is to protect her right flank going forward. It tells you a lot about the internal dynamics of the Republican Party these days, in which anyone who’s not conservative, very conservative, or wildly conservative must be a RINO who needs purging. Amid all the talk these days of Democrats “moving left,” the GOP remains the party where most pols avoid “the center” like the plague.