Rand Paul and Jeb Bush had their best debates. Bush clearly benefited from the absence of Trump–I guess it is an iron rule of forensics that your arguments go over better if someone isn’t making rude and dismissive faces while you talk. He was funny, relaxed, and together solid. But Paul and Bush are obviously in very weak positions in the race.
If Jeb got running room with Trump not on the stage, Cruz was denied oxygen. It certainly feels like he’s running behind here (although his internals evidently still have him ahead) and he was loaded for bear for Trump. Plus, Cruz perhaps does best in close combat, and there is great opportunity in being able to stand up to and best the Alpha Dog. Without Trump, Cruz was a little at sea.
The rest of Cruz’s night was good (and particularly admirable on ethanol), but in Trump’s absence a test for Cruz was if he could establish a frontrunner-worthy sense of dominance, and he didn’t.
I thought, as alluded to in the tweet noted by David, that Rubio was a bit off. By Rubio standards, I would give him a B. He would still benefit from talking slower, which contributed to the forced feeling of some of his riffs. The clips of his past statements on amnesty were brutal (the Cruz clips were tough, too). And lines that would usually generate applause didn’t get much reaction, although the crowd seemed a little muted generally.
As for Trump, we can’t know the effect of him sitting this one out. It certainly denied the proceedings electricity. It knocked out the Trump v. Kelly and Trump v. Cruz storylines, and limited the debate to the differences among the other candidates that feel as though they have already been extensively litigated, whereas there are arguments about Trump that still have not been vigorously pursued on the debate stage. Maybe next time, but by then Iowa will have voted, and we will know much more.