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

The 2024 presidential election has been underway for months, but with tonight’s first Republican primary debate in Milwaukee, we’re kicking off a new phase of the campaign. In these final five months before voting begins, we’re going to have monthly debates, dashes through Iowa, big-money fundraisers — and probably a culling of the field.

Tonight’s debate will feature eight candidates. Front-runner Donald Trump, who has a 37-percentage-point lead in FiveThirtyEight’s national polling average, will not be among them, as he has opted to skip the debate. Instead, we will hear from Florida Gov. Ron DeSantis; entrepreneur Vivek Ramaswamy; former Vice President Mike Pence; Sen. Tim Scott; former U.N. Ambassador Nikki Haley; former Arkansas Gov. Asa Hutchinson; North Dakota Gov. Doug Burgum; and former New Jersey Gov. Chris Christie.

There are a few threads and tensions we’re going to be watching tonight. First, in the absence of Trump, will his challengers’ attempts to position themselves as a more favorable option fall flat? How will candidates make their case for being a better alternative to Trump without having the contrast on stage beside them? Secondly, what sort of friction will we see between the anti-Trump candidates and those running on more similar ideas or rhetoric?

We’ll keep an eye on all this and more. You’ll be hearing from the crew at FiveThirtyEight and ABC News — as well as some new friends at PolitiFact — throughout the night. The Fox News-hosted debate begins at 9 p.m. Eastern, and we have some colleagues on the ground in Milwaukee who will ensure you’re going in with everything you need to know.

Thanks for joining us. Stay tuned as we update the blog with real-time analysis, charts, thoughts, questions, ideas, idle fancies and more. Leading up until the debate starts, we’ll run through the state of the race so far. Once the debate starts, we’ll make sure we’re addressing everything happening on stage, including what issues the candidates talk about, who they attack, how they position themselves and what Americans think.

-Analysis by Maya Sweedler of FiveThirtyEight