For the GOP, rightward ho!

The Republican Party is at war with itself. It’s divided over how best to shrink the federal budget and how to undo President Obama’s healthcare law. It hasn’t been notably successful at either, which helps explain why the GOP’s standing in the eyes of most voters has plummeted to depths not seen in three decades of modern polling.

None of this was planned, of course; parties don’t flirt with political suicide on purpose. But it wasn’t accidental either. Behind the GOP crackup over the government shutdown lies a much bigger battle for control of the party.

And the most important actors aren’t Sen. Ted Cruz (R-Texas) and the tea party members of the House who brought us the government shutdown. The party rift’s chief driver is a constellation of hard-line conservative fundraising groups, led in part by a former senator most Americans couldn’t pick out of a lineup, Jim DeMint of South Carolina.

When DeMint resigned from the Senate in January to become president of Washington’s Heritage Foundation, many were mystified; he was abandoning a safe seat with four years left in his term, all to run an aging conservative think tank across the street.

But DeMint has quickly turned Heritage — especially its new lobbying arm, Heritage Action for America — into a powerful engine of pressure on Republicans in Congress to move further to the right and reject almost any form of compromise with Obama.

“There’s no question in my mind that I have more influence now on public policy than I did as an individual senator,” DeMint told NPR recently.

It was Heritage Action that focused tea party conservatives in the House on the idea of using this fall’s long-scheduled votes on federal spending to try to “defund” Obamacare, and the group then organized a summer-long campaign (starring Cruz) to publicize the idea.

Meanwhile, the Senate Conservatives Fund, a separate political action committee that DeMint founded, played the role of enforcer, publicly attacking GOP members of Congress who didn’t fall in line. When Senate Majority Leader Mitch McConnell (R-Ky.) and other Republicans broke with the hard-liners on a procedural vote, the fund accused them of “betraying their principles.”

“Nobody worked harder to fund Obamacare in the Senate than Mitch McConnell,” the group said in a statement posted on its website and emailed to donors

The drive to defund Obamacare hasn’t accomplished much so far, but that doesn’t appear to worry Heritage Action’s 31-year-old CEO, Michael A. Needham, who said last week that the group’s long-term goal was to transform the GOP, which he called “the allegedly conservative party.” The government shutdown, he insisted, was a step on “a path to electoral success.”

After Mitt Romney lost the presidential election last year, Needham told a group of reporters that “the Republican establishment’s response … [was] to raise taxes, pass amnesty [by which he meant immigration reform], pass gun control and not fight on Obamacare.” Instead, he said, “The Republican Party should start authentically leading based on the values that their voters have” and “become a more populist party … that stands up for core conservative values.”

In other words, the party should oppose new taxes, immigration reform, gun control and, of course, Obamacare.

Heritage Action’s one concession to pragmatism so far has been an announcement that it wouldn’t oppose a short-term measure to lift the federal debt ceiling while budget talks continued.

There have been insurgent movements in American political parties before, of course. Goldwater conservatives broke with the party’s mainstream in 1964, and antiwar liberals divided the Democratic Party during the Vietnam War.

Those earlier movements, like this one, aimed to change their own parties first, on the assumption that voters wanted a purer form of politics.

But here’s what’s different about DeMint and his allies: They are eager to target Republican incumbents, even to the point of challenging them in Republican primaries. In addition to calling out McConnell, the Senate Conservatives Fund has denounced Sens. Lindsey Graham (R-S.C.) and Lamar Alexander (R-Tenn.), all of whom will face tea party primary opponents next year.

And DeMint is helping to build an impressive and apparently permanent infrastructure of fundraising organizations with the avowed goal of displacing the GOP’s traditional business backers. The goal, as Needham put it, is “to take on cronyism and the way K Street [lobbyists] run this town.”

But they should expect some push-back. Some of those K Street Republican lobbyists told me last week they were already organizing to support endangered incumbents, including McConnell, and plan to do some “primarying” of their own, funding moderate GOP challengers to several tea party members of the House, including two Michigan Republicans, Justin Amash and Kerry Bentivolio.

As a result, some of the toughest, most expensive campaigns in next year’s congressional election cycle may not be between Republicans and Democrats but in primaries that pit Republicans against each other — with the future of the GOP at stake.

Ronald Reagan, an icon to both sides in this fight, said to GOP volunteers in 1967: “There is room in our tent for many views. It is not your duty, responsibility or privilege to tear down or attempt to destroy others in the tent.”

Some of his heirs aren’t so sure.

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Twitter: @DoyleMcManus