Rich Lowry, National Review:
Tonight, finally, the other candidates began to play by Trump rules.
Rubio and Cruz interrupted, insulted, and mocked the Republican front-runner. Rubio obviously had the moment of the night, in the space of a couple of minutes exposing Trump’s utter vacuity on health-care policy, catching him repeating himself when Trump said he doesn’t repeat himself, and mocking Trump’s signature lines. Cruz was more prosecutorial and not as memorable but effective nonetheless. If I had any criticism, it was that they weren’t relentless enough and occasionally let up on the attack (this Peter Spiliakos post from a while ago nailed it). At one point, all three of the candidates were talking at once — this is what Trump has done, force everyone down to his level of reptilian politics where all that matters is trying to talk over people to establish your dominance.
It was very important that Rubio came out punching for his own image. If he had taken a pass on Trump tonight, he would have seemed incredibly weak and not a leader. Instead, he went toe to toe with him and won.