I think Geoffrey has this exactly right: It seemed a little like the candidates were playing pretend tonight by ignoring Trump. But they’re in a tough position, politically. Someone needs to go after Trump in order to open up space for another potential nominee, but going after Trump is also extremely unattractive to GOP voters. That combination keeps Trump in a strong position as the front-runner.

At this point, the question isn’t who will be the alternative to Trump, but whether Republicans will produce an alternative nominee to Trump at all. DeSantis needed to prove tonight that he could live up to the initial hype around him, that he was Republicans’ clear alternative to nominating Trump. But there didn’t seem to be a breakout moment for him. A handful of others — like Haley and Pence — had some strong moments, but we’ll have to wait for polling to see whether those actually resonated with voters. Otherwise, it’s more of the same – which is good news for Trump.

-Analysis by Leah Askarinam of FiveThirtyEight

It's not too surprising to me that Trump didn't come up much tonight except when explicitly pushed by the moderators. A lot of Republicans -- certainly GOP officeholders -- really don't like talking about Trump and never have. Tonight they were given the opportunity to pretend like Trump isn't in the race or the defining story of the election, and of course they took advantage of it. I bet it felt like a relief, even if it wasn't really moored in reality.
-Analysis by Jacob Rubashkin, Inside Elections

For the less-known candidates, debates are a crucial task to introduce themselves (in a positive light!) to the American people. The Google results posted here indicate that Ramaswamy made a big splash today (though I'm not sure how positive the reception will be). He and Scott currently have the strongest net favorable numbers among the GOP candidates. I don't think we heard enough from the latter candidate for his numbers to meaningfully change.

-Analysis by G Elliott Morris of FiveThirtyEight

Outside of the segment on Trump's indictments and his behavior on Jan. 6, it's been a bit surprising that there's been little discussion of him otherwise. There've been a few references to actions taken prior to Biden taking office, indirectly involving Trump, but not much specifically about him. That has turned this debate into something of an alternative universe where these are the main eight candidates, not the eight who are badly trailing the main guy not in the room.
-Analysis by Geoffrey Skelley of FiveThirtyEight