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’s 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 grass roots 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.”

Senate Republican leader Mitch McConnell of Kentucky said DeMint forced Washington to address economic issues.

“There is no question in my mind that he raised the profile of important issues like spending and debt and helped galvanize the American people against a big government agenda,” McConnell said in a statement.

Indiana Rep. Marlin Stutzman, R-3rd, said in a statement Thursday about Jim DeDeMint’s taking over as president of the Heritage Foundation for Ed Feulner, “The Heritage Foundation is trading one principled conservative stalwart for another.”

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.