WASHINGTON – Sen. Jim DeMint, patron saint of the tea party and a would-be Republican kingmaker, announced suddenly Thursday he would resign his South Carolina seat to head Washington’s conservative Heritage Foundation think tank — a shift that reverberated through a soul-searching GOP.

Just two years into a second, six-year term, DeMint said he would step down on Jan. 1 to helm Heritage while continuing the conservative fight.

The 61-year-old lawmaker, known to hurry home to South Carolina nearly every weekend, had signaled that this term would be his last, but his abrupt announcement shocked even his closest Republican colleagues.

“When he told me this morning, I about fell off my couch,” said South Carolina’s other senator, Republican Lindsey Graham. “I didn’t see this coming.”

Prizing ideology over electability, DeMint sometimes infuriated fellow Republicans, picking sides in GOP primaries with decidedly mixed results. He had no patience for centrist Republicans, pushing the party to the right while bankrolling candidates with millions from his political action committee, the Senate Conservatives Fund.

In 2010, candidates he ardently supported cost the GOP eminently winnable seats. This year, DeMint had better success.

“One of the most rewarding things I’ve done in the Senate is work with the grassroots to help elect a new generation of leaders who have the courage to fight for the principles of freedom that make this country so great,” DeMint said in his statement announcing his departure. “I’m confident these senators will continue the legacy of conservative leaders before them.”

DeMint also has sometimes been a thorn in the GOP side on legislation, just this week criticizing House Speaker John Boehner’s “fiscal cliff’ counteroffer to President Barack Obama that would raise tax revenue $800 billion as crushing for American jobs.

DeMint’s departure creates an opening for a new generation of hard-charging conservatives in the Senate — Rand Paul of Kentucky, Mike Lee of Utah and soon-to-be Sen. Ted Cruz of Texas.

The strong conservative element is pitted against the establishment as the Republican Party tries to figure out its next moves after this year’s defeat in the presidential race and the loss of congressional seats.

Shocked Senate Republicans were too courteous to say good riddance to DeMint, but a few made it clear that there were still hard feelings over the senator’s political moves.

“I won,” Sen. Lisa Murkowski, R-Alaska, said tersely when asked about DeMint backing her Republican primary rival Joe Miller in 2010, forcing her to run as a write-in candidate.

Democrats pointed out that they increased their numbers in this year’s elections and will hold a 55-45 edge in the Senate next year.

“His effect on the system may have been more beneficial to Democrats than to Republicans,” said Sen. Chuck Schumer, D-N.Y.

Sen. John Cornyn, R-Texas, who headed the National Republican Senatorial Committee in 2010 and this year, said he and DeMint agreed as conservatives “on 95 percent of the issues, it’s a lot of it has to do with tactics to advance the conservative cause through the electoral process. I wish him well.”

Delaware and Colorado in 2010 are sore points for Republicans who were certain they could win the Democratic-held seats.

DeMint backed Christine O’Donnell who prevailed over the more electable Rep. Mike Castle in the GOP primary; Democrat Chris Coons easily beat O’Donnell that November.

In Colorado, DeMint supported conservative Ken Buck who stumbled in his race against Democratic Sen. Michael Bennet.

Yet for the defeats, there are several Republicans who owe their seats to DeMint, and they expressed appreciation for a man they consider the chief instigator of the tea party movement.

“We have a much bigger liberty caucus in the Senate than we did before,” Paul said. “I think a lot of that is thanks to Jim DeMint.”

Said Florida’s Marco Rubio: “I would not be in the U.S. Senate had it not been for Jim DeMint taking a shot on me.”