Rick Santorum, that's who! So, naturally, Santorum is leading in two of the three caucuses held tonight—Minnesota and, especially, Missouri. Romney leads in Colorado, where he won in 2008 with more than 60% of the vote. Pertinent questions include:

· Are we looking another Santorum surge right in the face?

· Will Ron Paul continue to underperform?

· Will Gingrich do worse than expected? If so, is that a sign that last week's weird performance was his last chance with voters?

· Is Mitt Romney completely off-putting for middle-class Republicans?

Tonight we'll find out! Results will start pouring in at 5 pm, PST.