THE EFFECT OF FRINGE SUCCESSES…. With the primary season effectively over, and the far-right GOP base overriding the party establishment’s judgment on more than a few occasions in recent months, it’s pretty clear the Republican mainstream has been replaced with extremists and hard-line ideologues. The question, though, is whether this will matter.

E.J. Dionne Jr., who believes the GOP has been “reduced to nothing but its right wing,” noted that the pertinent question now is “whether the country is ready to deliver a majority to a Republican Party that now holds problem-solvers like [Mike] Castle in contempt [and] is scared to death of a well-financed right wing that parades under a false populist banner…. Will moderate voters take a chance on the preposterous proposition that this Republican Party will turn around and work in a calm, bipartisan way with President Obama?”

The answer isn’t obvious. Josh Green said this week that the radicalism of the Republican Party may matter a great deal, especially if “independent voters start to ascribe the views of Tea Party candidates like O’Donnell to Republican candidates in general.” Clive Crook added, “A party that nominates O’Donnell is a party unfit to govern. Many centrists and independents, previously ready to swing over to the Republican side, are likely to take that view.”

David Brooks thinks all of this is backwards.

Many of my liberal friends are convinced that the Republican Party has a death wish. It is sprinting to the right-most fever swamps of American life. It will end up alienating the moderate voters it needs to win elections.

There’s only one problem with this theory. There is no evidence to support it. The Republican Party may be moving sharply right, but there is no data to suggest that this has hurt its electoral prospects, at least this year. […]

In Ohio, Republican Rob Portman has opened up a significant lead on his Democratic opponent. In Kentucky, Republican Rand Paul is way ahead, as is Marco Rubio in Florida. In Illinois, Republican Mark Kirk has a small lead, and Linda McMahon has pulled nearly even in Connecticut. Sharron Angle, a weak candidate, is basically tied with Harry Reid in Nevada.

That’s not a bad pitch, but it’s unpersuasive. Most of Brooks’ own examples actually tell a different story than the one he perceives — Paul is ahead in Kentucky, but the race wouldn’t be competitive if Republicans hadn’t nominated an extremist. Rubio is leading in Florida, but had the party not driven Charlie Crist from its ranks, the incumbent governor would be cruising past Kendrick Meek and the race would be off the board. Angle is both “weak” and “effectively tied,” but had the GOP nominated someone sane, Nevada would have been a sure-fire pick up for Republicans.

What Brooks sees as examples of extremism having no meaningful effect are actually examples of Tea Party zealots creating competitive races where there would have been smooth sailing for the GOP.

What’s more, Election Day isn’t tomorrow. Opinions are still taking shape; Republicans still aren’t gaining in popularity; and voters are just starting to notice the radicalization of a major political party after a decade of that party’s spectacular failures.

I’m reluctant to draw any hard conclusions here; the season may yet take a couple of twists and turns. For that matter, the midterms may very well come down to Democratic Congress + weak economy = electoral ruin for the majority, and the GOP’s extremism will be rewarded despite itself.

But the Republican Party’s decision to “sprint to the right-most fever swamps of American life” may yet carry consequences Villagers haven’t considered. Using Brooks’ examples, it already has.

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.