As you watch the debate, keep an eye on which candidates separate themselves from the crowd. That’s because right now, the Republican presidential primary is not so much a race for first place as it is for second and third. FiveThirtyEight’s latest average of national GOP primary polls has Trump at 52 percent of the vote among likely Republican primary voters. DeSantis is a distant second at 15 percent, Ramaswamy is at 10 percent, Pence and Scott are at 4 percent, and Haley and Christie are at 3 percent. Everyone else is below 1 percent.

Trump’s lead will be very hard for the other candidates to close — so their best hope at this point is to stay in the game, in case Trump drops out (unlikely as that seems right now) or something else changes. DeSantis is currently in position to be the would-be front-runner if Trump drops out, but depending on debate performances and other factors, he could wind up in a close race with one of the other candidates currently clustered in that 5-10 percent range.

-Analysis by G. Elliott Morris of FiveThirtyEight

Chris LaCivita, a senior campaign adviser to Trump, said on the conservative “Ruthless” podcast streamed live before the debate that Trump does not currently plan to attend the second GOP debate, set for next month in California, but indicated that Trump could change his mind.

"He's not going to be in California ... Well, first of all, with President Trump, you know, he could change his mind at any moment … And you should just assume that he won't until he does,” LaCivita said.

Both fellow primary candidates and GOP officials have urged Trump to be on the debate stage, although some candidates have downplayed the significance of his absence.

-ABC News’ Laura Gersony

Hours before eight Republicans take the debate stage, Democrats appear to be going on offense around the site of the event.

The Biden campaign rolled around a mobile billboard around Milwaukee’s Fiserv Forum which depicts “Dark Brandon” -- President Joe Biden’s satirical alter ego.

The billboard hits Republicans on their abortion positions, particularly their support for restricting the procedure.

-ABC News' Fritz Farrow

Trump campaign surrogates like Rep. Marjorie Taylor Greene, R-Ga., have been spending the day on media row touting Trump’s policies to various news outlets. She has plans to host a post-debate analysis show with Rep. Matt Gaetz, R-Fla., on conservative outlet Right Side Broadcasting Network.

Donald Trump Jr. and Kimberly Guilfoyle have also been live-streaming for his podcast outside the debate arena since Wednesday afternoon, joined by other Trump surrogates like Greene, Gaetz, and Kari Lake.

On the podcast, Donald Trump Jr., Guilfoyle and various surrogates sought to downplay the debate, calling the stage a “VP debate,” a “kids’ table” at a Thanksgiving dinner, and a “secretary of education debate.”

Other candidates have criticized the former president for declining to face them and make his pitch to voters in Milwaukee.

Lake on the Donald Trump Jr. podcast also said she spoke with the former president earlier on Wednesday afternoon about the pre-taped Tucker Carlson interview scheduled to be released Wednesday, saying it will be a “good interview.” She said the elder Trump sounded “really good” in the afternoon but told her that “things are going to get worse before they get better.”

-ABC News' Soo Rin Kim and Lalee Ibssa

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