Tonight I’m on Pence and Hutchinson duty. Neither candidate appears to have a great shot at winning the primary — the former vice president is at 4 percent in FiveThirtyEight’s national polling average while the former Arkansas governor hasn’t even garnered 1 percent — but Pence at least has a decent chance of making a debate-night splash. Given the events of Jan. 6, 2021, Pence has the strongest claim to the anti-Trump “lane” of the primary. I wouldn’t be surprised if we saw some real fireworks between him and the GOP candidates who have been quick to jump to Trump’s defense after the bad news he has been hit with over the past year. For his part, Hutchinson will have to pull off a masterclass in persuasion and performance to gain substantial ground. In our poll with Ipsos and The Washington Post, only 6 percent of Republicans said they were even considering voting for him, much less were intending to do so. In a more fluid primary, he’d maybe have a shot at doing something about that. But with Trump as the default and other candidates leading the various anti-Trump lanes, those are really tough numbers to come back from.

–Analysis from G. Elliott Morris_

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

Before tonight’s debate kicks off, FiveThirtyEight, The Washington Post and Ipsos partnered to ask Republican voters about how they might vote in the upcoming Republican presidential primaries. Specifically, we asked 4,968 likely Republican voters which issues are most important to them when deciding which candidate to vote for in the primaries, using Ipsos’s KnowledgePanel.

We offered respondents a list of 16 issues and allowed them to select up to three. Of the topics that we asked about, voters were most concerned about “getting inflation or increasing costs under control” (53 percent of respondents selected this issue), something Republican voters have been concerned about since at least the 2022 midterms, according to a previous FiveThirtyEight/Ipsos poll. Other issues that were top of mind for voters were “controlling immigration” (36 percent), “someone fighting against liberalism and the woke agenda” (25 percent) and “ability to beat Joe Biden” (25 percent).

If tonight’s debate touches upon those top issues, voters might get some clarity on who they are considering voting for when primary season comes around.

-Analysis by Holly Fuong of FiveThirtyEight