The question from last week’s sudden shift in momentum towards Herman Cain in the GOP presidential primary race was whether Cain could actually vie for the nomination. After today’s poll from the Washington Post and ABC, the question may be whether anyone but Mitt Romney could stop him. Right now, it certainly doesn’t like Rick Perry could, whose fortunes have fallen faster than they rose after two bad debates: After a quick rise in the race for the Republican presidential nomination, Texas Gov. Rick Perry has experienced an almost equally dramatic decline, losing about half of his support over the...