CLUB FOR CONSERVATIVE FEALTY…. One might expect congressional Republicans to be a little less disciplined under the circumstances. When a popular president wins by a wide margin, and governs during a crisis with a popular agenda, it stands to reason the minority party might be at least a little splintered — especially among those representing states or districts the rival party’s president just won.

But that hasn’t happened, and there’s been near unanimity among Republicans in opposition to President Obama’s economic recovery package and budget (among other things). Where’s all of this party discipline coming from, especially in a party with no clear leadership?

Chances are, the Club for Growth has had something to do with it.

Pennsylvania Sen. Arlen Specter’s switch to the Democratic Party underscores the clout of Club For Growth, a conservative group that targets Republicans it brands insufficiently committed to low taxes and small government.

The move also has inflamed a debate within the party: Are the group’s tactics good or bad for Republicans?

Mr. Specter fingered Club For Growth as the key factor behind his decision, saying he would have lost the Republican primary to a Club-backed rival. His decision has prompted some Republicans to turn on the organization, saying it backs those who are so conservative that they then lose to Democrats.

“If their goal is to increase the Democrats’ numbers in Congress, they’re doing a very good job,” said Rep. Steven LaTourette (R., Ohio), a moderate who won his seat in 1994. “Do they want a permanent minority of 140 people as pure as Caesar’s wife, or a Republican majority that can get them 70% of the issues that are important to them?”

Not surprisingly, the Club for Growth believes Republicans would be wildly successful nationwide, if only every member of the party would agree to cut taxes, slash spending, and reject every Democratic economic idea. The group’s leadership really seems to believe the nation is made up of Grover Norquists from coast to coast, and the GOP is in a deep hole because it’s just too darn liberal.

The result is an outfit that launches very aggressive primary challenges against key Republican officeholders who stray from the Club for Growth’s vision.

It’s why DCCC Chairman Chris Van Hollen (D-Md.) told the WSJ that every time they see the Club for Growth take on a Republican, “it brings a smile to our face.”

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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.