BEHIND THE GOP SMILES IN THE SENATE…. Throughout the modern political era, when there’s a “wave” election that sweeps one party out of power in the U.S. House, it also tends to lead to a new majority in the U.S. Senate. We saw this in 2006, 1994, and 1946.

But you’ll notice this trend did not hold true in 2010. Republicans hoped to take back the Senate — a week ago, Sen. James Inhofe (R-Okla.) practically guaranteed it would happen — but fell far short. While several pre-election forecasts showed them gaining eight seats, and some party leaders predicted a net gain of nine, at this point, it looks like they picked up six.

To be sure, a six-seat pick-up is hardly a bad cycle. On the contrary, it’s a significant turn-around for the GOP. But it looks rather puny compared to the party’s House gains, and as a historical matter, six seats isn’t especially extraordinary. It doesn’t even match the party’s 1994 gains.

And yesterday, some of the Republican frustrations about this worked their way to the surface.

Long-simmering tensions within the Republican Party spilled into public view Wednesday as the pragmatic and conservative wings of the GOP blamed each other in blunt terms for the party’s failure to capture the Senate.

With tea party-backed candidates going down in Delaware, Colorado and Nevada, depriving Republicans of what would have been a 50-50 Senate, a bloc of prominent senators and operatives said party purists like Sarah Palin and Sen. Jim DeMint (R-S.C.) had foolishly pushed nominees too conservative to win in politically competitive states.

Movement conservatives pointed the finger right back at the establishment, accusing the National Republican Senatorial Committee of squandering millions on a California race that wasn’t close at the expense of offering additional aid in places like Colorado, Nevada and Washington state, where Democratic Sen. Patty Murray holds a narrow lead as the votes continue to be counted.

I’m not inclined to interfere with the intra-party squabbling, but can’t they both be right?

The “pragmatic” wing is right that Delaware, Colorado, and Nevada were entirely winnable, but thanks to the Palin/DeMint crowd, some of the year’s most extreme candidates won GOP nominations and lost. As a consequence, what would have been a 50-50 Senate split next year will be a 53-seat majority for Democrats. (Trying to get Lieberman and Nelson to switch wouldn’t even make a difference.)

“Candidates matter,” said Sen. Lindsey Graham (R-S.C.). “It was a good night for Republicans but it could have been a better one. We left some on the table.”

The “purist” wing is also right that the National Republic Senatorial Committee invested $3 million of scarce resources into California’s Senate race for no apparent reason. Party officials seemed to think Carly Fiorina (R) really could pull the upset, but the NRSC was wildly wrong — she lost by a wide margin. Could that $3 million have made more of a difference in, say, Colorado and Washington? Probably.

I’d be surprised if these disputes lingered too much longer — the Senate Republican caucus has a wrecking ball to polish — but the fight is something to keep an eye on. At a minimum, the party is already putting plans for 2012 in place, and if they conclude the 2010 strategy was flawed, they’ll try to correct it.

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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.