I’m watching DeSantis tonight. The Florida governor really needs a good performance tonight to reestablish himself as the main alternative to Trump after seeing his national polling average slip from 36 percent in mid-March to just 15 percent today. It will be interesting to see how much he goes after the absent Trump — which has typically been his strategy to this point — versus attacking the other not-Trumps, who are realistically his main competition these days. I’m also curious what bar DeSantis will be measured against. The popular narrative about him is that he’s kind of awkward, so maybe a quote-unquote “presidential” performance will be reassuring to people who are on the fence about him. But our poll with Ipsos and The Washington Post actually found that voters have relatively high expectations when it comes to DeSantis’s debating abilities, so maybe he needs a truly masterful performance in order to move the needle.

–Analysis from Nathaniel Rakich

Attendees seen greeting supporters outside the debate hall in Milwaukee have included former Arizona gubernatorial candidate Kari Lake, Georgia Gov. Brian Kemp and Trump's son Donald Trump Jr.

While Ramaswamy is still "unlikely" to visit the spin room following the debate, his wife, Apoorva Ramaswamy, his communications director and senior adviser Tricia McLaughlin, two other team members and an undisclosed "special guest" will be there on his behalf, according to McLaughlin.

The spin room is the space where campaigns highlight their candidate and attack their opponents after the debate. Many candidates themselves head there after they take the stage.

-ABC News' Kendall Ross

In anticipation of tonight’s debate, we partnered with Ipsos and The Washington Post to ask likely Republican primary voters what they think about tonight’s debate participants and the candidate field in general.

The 4,968 likely Republican primary voters we polled using Ipsos’s KnowledgePanel expect Ramaswamy’s performance to be best among the eight expected debate participants. According to a five-point scale that we calculated using respondents’ answers (with 1 being “terrible” and 5 being “excellent”), likely voters expected Ramaswamy to perform “very good” (3.59 out of 5). They thought DeSantis would perform second-best (3.51 out of 5) and Scott third (3.43 out of 5).

When it comes to whom respondents think they’ll place their votes for in the primaries, 65 percent are considering Trump and 52 percent are considering DeSantis. About 1 in 4 likely Republican primary voters are considering voting for Pence, Scott and Haley. The remaining six candidates we asked about fell below 25 percent.

We’ll be watching to see how the candidates fare tonight, and if debate watchers’ opinions on whom they’re considering voting for will change after tonight’s performances.

-Analysis by Holly Fuong of FiveThirtyEight