Caucus process is good for Rubio. He is palatable to a lot of people who looked around and saw that their candidate wasn't viable.
I felt that he was going to over perform once I heard that a lot of GOP voters had recently made up their mind and knew that likely meant the safer choice in Rubio. Cruz and Trump voters don't appear to be the type to vacillate. Clinton should be a little more wary of Sanders, at this point, too.