"Our country is in decline," DeSantis said in response to the first debate question, on the economy. "This decline is not inevitable. It's a choice. We need to send Joe Biden back to his basement and reverse American decline."

DeSantis also took a swipe at the president's son Hunter, criticizing Hunter for selling high-priced artwork while other people are struggling to afford groceries.

"It starts with understanding we must reverse Bidenomics so that middle-class families have a chance to succeed again," DeSantis said, referring to the name that the White House has used to popularize what they see as the president's successful platform.

I am here in Milwaukee in the spin room. If you think journalism is glamorous, let me disabuse you of that notion. The media is being housed in what is essentially a parking garage at the FiservForum and the bathrooms are outside porta-potties. By the way, it was a 100-degree day in Milwaukee, so just going to the bathroom is a bit of an experience. And yes, I would like some Wisconsin cheese with my whine. Anyway, I'll be quiet about the plight of the reporters, we are here to hear about the plight of Americans and what these candidates have to say about it. Let's begin!
–Analysis from Galen Druke of FiveThirtyEight

The Biden-Harris campaign appeared to buy airtime on Fox News ahead of the GOP primary debate, with ad advertisement for the Democrats’ reelection campaign running just minutes before the eight Republican hopefuls took the stage.

The ad, which acted as something of counter-programing to what the GOP hopefuls may discuss during the two-hour debate, touted what the Biden administration sees as its legislative accomplishments, like the American Rescue Plan, the Inflation Reduction Act, the CHIPS and Science Act and the Bipartisan Infrastructure Law.

The spot highlighted the economy under Biden, which is likely contrary to what the Republican primary candidates will raise on stage -- citing Biden's low marks from voters on his handling of economic issues.

–ABC News’ Isabella Murray

I’m monitoring Christie and Scott tonight. Even though the two candidates are polling similarly in the 3 to 4 percent range in FiveThirtyEight’s national polling average, they are a subject in contrasts. Although Pence has been more vocally critical of Trump recently, Christie is the most high-profile, full-on anti-Trump candidate on stage. Realistically, Christie has very little chance at the GOP nomination because he has negative net favorability ratings among Republicans. But that may mean he will focus almost entirely tonight on attacking Trump rather than making appeals to the party base. As a result, Christie could be a popular foil for the contenders on stage who have largely eschewed going after Trump, or have even defended him.

Meanwhile, Scott arguably has one of the highest ceilings of any candidate on stage. He’s not nearly as well-known to GOP voters as Trump or DeSantis, but Scott gets rave reviews from Republicans who are familiar with him. That means tonight is an opportunity for him to expand his reach and also potentially increase the share of GOP primary voters who would consider voting for him. I’ll be interested to see how much he leans into his “happy warrior” image as a means of differentiating himself from DeSantis and Ramaswamy, and whether he tries to rise above the fray to some extent if some of the other candidates — especially Christie — get into verbal fisticuffs.

–Analysis from Geoffrey Skelley

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