Republicans aren’t shy about lobbing the “class warfare” charge at Democrats. But now Newt Gingrich is aiming those words at Mitt Romney over Romney’s idea to scrap or limit the mortgage-interest deduction for second homes. Romney, the Republicans’ all-but-certain presidential nominee, told donors in Florida last weekend that he’d take away the deduction for high-income earners. His campaign later said it was just an idea, not a hard-and-fast policy. But Gingrich took it as gospel. “Governor Romney’s proposal to limit certain tax deductions based on income, including the deduction for mortgage interest on second homes, is a surrender to the...