If two-term Massachusetts Gov. Deval Patrick wants to be a candidate for president in 2016, he’s faced with one problematic detail: We’ve already had a black president. Patrick, who’s the Bay State’s first African-American chief executive, is openly chewing on a bid for the White House, answering “maybe” in a recent Politico interview when asked about a possible run. “That’s a decision I have to make along with my wife of 30 years, and she’s a tough one to convince,” he said. “Let’s just see what time tells.” The problem, though, isn’t so much convincing his wife—who’s probably attracted now,...