Mitt Romney lost the primary in Missouri, and failed also in Colorado and Minnesota. Colorado he won in 2008. He has a decided enthusiasm gap. Nonetheless, he made little effort in these states (v. the 13,000 mostly anti-Gingrich ads he ran in Florida) and he is expected to win Mormon-heavy Arizona and his dad's state of Michigan in the near future.
Romney is still the favorite to win, as Southerners don't like Santorum and Yankees don't like Gingrich. If he can get into a two person race with Obama, then all his money and vote stealing can come to the fore.