Jim DeMint, Tea Party US senator, quits
US Republican senator and Tea Party champion Jim DeMint is resigning to lead a conservative think tank.
His office said the South Carolina politician would become president of the Heritage Foundation next month.
The 61-year-old Republican was first elected to the Senate in 2004 and won a second term in 2010.
South Carolina's Republican Governor, Nikki Haley, will appoint his successor, who will serve until a 2014 special election.
'Conservative rock star'
As the state is solidly Republican, the balance of power is not expected to change in the Senate. Democrats have 55 of the 100 seats in the upper chamber.
In a statement, Gov Haley said: "On a personal level, I value Jim's leadership and friendship. Our state's loss is the Heritage Foundation's gain."
Sen DeMint's current salary is $174,000 (£108,000), while the outgoing leader of the Heritage Foundation reportedly earns $1m.
In a statement, Sen DeMint said he believes he will be able to share his conservative views with a wider audience at the think tank.
"I'm leaving the Senate now, but I'm not leaving the fight," he said. "I've decided to join the Heritage Foundation at a time when the conservative movement needs strong leadership in the battle of ideas."
Republicans in his home state were stunned by the resignation.
South Carolina party chairman Chad Connelly said: "He's been a conservative rock star.
"I'm sure the conservatives in South Carolina will be heartbroken. DeMint's been an icon for a lot of us in the conservative movement."
Popular with Tea Party activists, Sen DeMint at times clashed with the Republican leadership.
Only this week, he rebuffed Republican House Speaker John Boehner's proposal during fiscal cliff negotiations that offered $800bn in new taxes.
Sen DeMint said Mr Boehner's offer would "destroy jobs and allow politicians in Washington to spend even more, while not reducing our $16tn debt by a single penny".
The senator - who previously served in the US House of Representatives for three terms - also led opposition to President Barack Obama's healthcare reform.
"If we're able to stop Obama [on healthcare]," Mr DeMint said in 2009, "it will be his Waterloo."
But the healthcare reform became law in 2010 and was upheld by the US Supreme Court this year.
Sen DeMint also helped set up a political action committee to back Senate candidates whom he deemed to be bona fide conservatives.
He supported Christine O'Donnell in Delaware and Sharron Angle in Nevada, although both were soundly beaten after adopting stances widely viewed as beyond the mainstream.
But Sen DeMint was also one of the first to champion Florida Senator Marco Rubio, now a rising Republican star.
Sen DeMint had already said he would not run for re-election, but his announcement to step aside earlier was a surprise.