Here's my analysis: Republicans are tired of tongue-tied, deer-in-the-headlights candidates. They're tired of gaffes and weasel-worders and stammering apologists and candidates who always need to have their words clarified by handlers. They're tired of candidates who can't debate or think on their feet or answer complicated and embarrassing questions. They're tired of watching presidential debates with their hearts in their mouths.
They compared the way Gingrich answered the question about his ex-wife to the way Romney answered the question about his tax returns and they decided that they'd rather have Gingrich go up against Obama.
It's high-wire-act fatigue. And they may have made the right choice.