A PARTY REAPS WHAT IT SOWS…. Congressional Republicans haven’t played a constructive role in policymaking over the last couple of years, in part because they disagree so strongly with Democrats, but there’s more to it than that. They’ve also boxed themselves in — after a party condemns a president as an illegitimate Communist intent on destroying on America, the party has left itself very little room for compromise.

Indeed, based on its own larger attack strategy, how can the GOP be expected to find common ground with a policy agenda it considers un-American? It’s how we go from the GOP agreeing with 80% of the Democratic health care plan to the GOP considering the same plan “Armageddon.” Republicans have positioned themselves in such a way as to make working with those who may disagree with them largely impossible.

But this dynamic is not limited to policymaking. Jon Chait explained overnight how this attitude — the GOP have characterized their efforts as “a twilight struggle to save the last vestiges of the Republic” — applies to campaign politics.

The premise of all these pleas for [Mike Castle in Delaware’s Republican Senate primary] was extremely sensible: this is politics. Sometimes you move the ball forward, sometimes the other team moves it forward. Sometimes you make compromises in order to get ahead.

But the Republican base has been taught not to think this way. This isn’t just politics, remember? This is a twilight struggle for freedom. And Mike Castle didn’t just cast a couple bad votes. He acquiesced in a sinister plan to undermine capitalism. How could they ever support a candidate like that?

Quite right. These voters have been told by their party not to compromise or settle for partial victories. There’s just too much at stake, they’re told. Evil forces are trying to take your country away.

Easily misled and manipulated people bought into this rhetoric. They’ve come to believe it’s their responsibility to elect radical ideologues who’ll save us from impending doom. Sensible people with last names like Castle, Crist, Specter, Bennett, Murkowski, and Inglis were insufficiently right-wing, so they were cast aside.

These activists have been fed red meat that’s been tainted without their knowledge — and now those who did the tainting are frustrated when the activists end up sick.

There’s a limit to this, of course. Republicans are still poised to have an exceptionally good election cycle, and many of the lunatic candidates who’ve won primaries without the party’s backing are very likely to win anyway.

But stepping back, even with the GOP’s expected gains in mind, Republicans’ carefully-executed strategy will leave them with (a) fewer wins than they would have had; (b) a smaller, more extreme party; (c) a base that’s been taught to reject any and all compromises; and (d) a party incapable of governing effectively.

As I said earlier, Frankenstein didn’t like his monster very much, but he still had to live with the consequences.

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.