Why did Trump go after Rubio so hard tonight, as opposed to Cruz?
Cruz has done very well so far, (if you can call three out of 16 or so states “very well”), but looking forward he’s not doing so good. He’s doing very poorly in Florida, and very poorly in Ohio. Even in Louisiana, which you’d think would be a Cruz friendly state, he’s behind by almost 20 points.

Trump wins for sure if either Cruz or Rubio goes down. Between the two, Rubio is the easier target. It makes sense to knock him out now and lock up the win.