While Mitt Romney has remained a constant in polling for the Republican presidential nomination at around 25-28%, inconstancy has been the constant among his opponents. Michele Bachmann became the first to ride a wave to Romney’s relative polling position, only to fade when Rick Perry entered the race. Now Perry has faded after a series of awful debate performances and Herman Cain has taken his place for the last six weeks. If Cain can’t maintain his momentum, who will be the next Not-Romney? Byron York reports from Iowa that it may well be Newt Gingrich: For days, there’s been talk...