WASHINGTON — Influential conservatives said Wednesday that Mitt Romney’s naming of Sen. Jim DeMint as a national chairman of his presidential campaign will help the former Massachusetts governor woo bedrock Republicans in South Carolina and beyond. Romney named DeMint one of three national co-chairmen, along with Sen. Judd Gregg of New Hampshire and Missouri Gov. Matt Blunt. Romney, who has moved into the top tier of GOP White House candidates, said the three men “bring an incredible depth of knowledge and experience to our campaign to build a stronger America with a stronger military, stronger economy and stronger families.” David...