Half of likely voters now prefer Mitt Romney for president and 46 percent back President Barack Obama, according to the latest interview data from Gallup. "While Romney's four-percentage-point advantage is not statistically significant, he has consistently edged ahead of Obama each of the past several days in Gallup's seven-day rolling averages conducted entirely after the Oct. 3 presidential debate," Gallup said. "With three weeks to go in the campaign, Obama appears to be losing momentum, and now trails Romney by four percentage points among likely voters," Gallup said. "That contrasts with his seven-point win over McCain in 2008. Given the shift in overall voter preference, it follows that Obama will have lost support among at least some subgroups of the electorate. Those losses are not proportionate across all subgroups, however. He shed the most support among Southerners, college graduates, postgraduates, 30- to 49-year-olds, men, and Protestants. He also lost a moderate amount of support among whites, Easterners, women, and Catholics -- while not building new support elsewhere."