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

Yeah, Maya, I am surprised Trump didn’t come up more. With him not on stage, I actually thought it would be easier for the candidates to swipe at him, since there was no risk of him punching directly back. But with some notable exceptions, like Christie and Hutchinson (and even then, only on a couple occasions), the candidates showed little interest in hammering away at the primary front-runner. I think that’s a questionable strategy since none of these candidates will be able to earn majority support in the primary without stealing some of it from Trump.
-Analysis by Nathaniel Rakich of FiveThirtyEight

In the aftermath of a debate, it can be hard to figure out the actual impact of a viral moment or heated exchange. Here are some data-driven approaches that can help cut through the noise:

First, ignore “instant polls” that ask questions only among people who watched the debate. That group is not likely to represent the feelings of the broader population. Instead, look for post-debate polls — (like ours with Ipsos and the Washington Post) — that ask questions among the same group of Americans both pre- and post-debate.

Second, in the days following the debate, look at data that captures attention to candidates, such as trends in search results or media coverage, to determine which candidate made the biggest splash. Media attention is crucial for candidates who aren’t well known to gain traction in the polls and with donors.

Finally, look for changes in horse-race polls in the week or two after the debate. There is a lot of noise in primary polls (especially this time around) and it can take some time for changes in public opinion to be reflected in our polling average.

The big thing to remember is that what’s important to journalists and television pundits may not be what’s important to the public, and we have to wait for pollsters to ask them how they feel.

-Analysis by G. Elliott Morris of FiveThirtyEight