Jim DeMint has announced his intention to resign his Senate seat to head up the conservative Heritage Foundation. I am not sure if this is a good thing or bad thing but at least he is out of the Senate.
He has promoted tea party candidates in Senate primaries in the past against more electable centrists. Some of these tea party candidates ended up losing winnable seats, eg Christine O'Donnell. He is probably the single most important reason why the Republicans didn't gain control of the Senate in either of the last two elections. He had promised not to get involved in primaries for the 2014 elections but now that he has a different role, it remains to be seen if he keeps that pledge. He has always been a purist as conservatives go and stymied things like immigration reform.
This won't affect the arithmetic in the Senate and the Governor Nikki Haley is a Republican and will appoint a successor until the next election in 2014.
Hopefully DeMint will be less influential now that he is out of the Senate.
Jim DeMint to resign to head Heritage Foundation - Manu Raju and Scott Wong - POLITICO.com