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

Recent election cycles have shown how debates can substantially alter a candidate’s trajectory. The debates won’t always do this, of course, and early primary polls remain relatively predictive of who will end up winning a party’s nomination. However, a candidate can earn a real polling bounce from a debate — or fall into a valley.

Primary polls are inherently more volatile than general election polls. In a general election, most voters already lean toward one party, so only a small part of the electorate is likely to shift its views over the course of a campaign. But in a primary, voters in one party may be open to multiple candidates because most contenders will share similar views on a number of issues. As a result, exposure to an unfamiliar candidate could prompt voters to begin considering that contender, while a strong or weak performance by a candidate they do know could make them look elsewhere.

For example, early in the 2012 cycle, Texas Gov. Rick Perry appeared to be now-Sen. Mitt Romney’s most serious opponent for the Republican nomination. But in a September 2011 debate, Perry defended a Texas policy that gave undocumented immigrants access to in-state college tuition. The backlash from the GOP base came swiftly, as Perry fell out of contention in the polls, well before a later debate in which he — oops — forgot the name of the third of three federal agencies that he aimed to dismantle as president. Four years later, former tech executive Carly Fiorina had very little support early in the 2016 Republican race, but in August 2015 she stood out in an “undercard” debate. Her polling numbers improved and she made the main stage in subsequent debates, giving her a platform that eventually led Texas Sen. Ted Cruz to make her his vice presidential pick in a last-ditch attempt to rally support against Trump in the 2016 primary.

-Analysis by Geoffrey Skelley of FiveThirtyEight