The U.S. Senate will lose one of its most influential – and controversial – conservatives when Jim DeMint resigns in January, as he seeks a national audience for his ideas at The Heritage Foundation.

And South Carolina will lose a junior senator who overwhelmingly won re-election in 2010.

The selection of DeMint to head the nation’s leading conservative think tank is an indication of just how prominent he has become as an advocate of limited government and fiscal frugality. Indeed, the Greenville Republican emerged in recent years as a national figure in articulating the views of the tea party, a movement that powered the GOP’s capture of the U.S. House in 2010.

DeMint’s departure won’t add to the Democrats’ margin of power in the Senate, since Republican Gov. Nikki Haley will appoint a replacement to serve until the next general election.

After some initial hesitation, DeMint decided to abide by his pledge to make this second term his last.

But by running for a second term, he implicitly pledged to complete it, barring disability. That makes his abrupt departure a disservice to those who supported him at the polls in 2010 in the justified expectation that he would serve through 2016. ...

Meanwhile, speculation immediately focuses on Haley’s selection of our next senator, who will serve through 2014. She said she does not want the job herself.

DeMint reportedly wants her to deem 1st District Rep. Tim Scott as his successor. Now preparing for his second term, Rep. Scott has shown strong conservative credentials. In the next session he will be the House’s only black Republican.

Another familiar name in the rumor mill is former S.C. Attorney General Henry McMaster, who ran against Haley in the 2010 GOP primary before supporting her in the runoff.

Others on the short-list include Jenny Sanford, former wife of former S.C. governor Mark Sanford; Catherine Templeton, S.C. public health and environmental control agency director; and U.S. Rep. Trey Gowdy, a former Spartanburg prosecutor.

Former House Speaker David Wilkins of Greenville, who served as U.S. ambassador to Canada, shouldn’t be counted out.

Regardless of whom the governor chooses, let’s hope our next junior senator blends a fiscally conservative ideology with a practical ability to distinguish between wasteful pork and necessary federal spending.