Businessman Herman Cain has risen to the top of a national poll of Republican primary voters, upending the GOP field yet again this cycle. Cain has the support of 30 percent of Republicans in the Public Policy Polling survey, trailed by Mitt Romney at 22 percent, Newt Gingrich at 15 percent, and Rick Perry at 14 percent. Cain is also the second choice of 24 percent of those polled — the highest of any candidate. In a two-person race, Romney would lead Perry 48-38, Cain would lead Romney 48-36, and Cain would destroy Perry 55-27. The poll was conducted before...