After a campaign effort that has defied convention and angered top Iowa Republicans, Mitt Romney is well-positioned to emerge as a big winner in Tuesday's presidential caucuses. The tightest GOP caucus contest in decades features Romney, Ron Paul and a fading Newt Gingrich in a virtual tie for the lead, making the final days of politicking unusually consequential. And another candidate, Rick Perry or Rick Santorum, could get hot at the end and knock one of the favorites out of the top three.