"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

In the aftermath of a debate, it can be hard to figure out the actual impact of a viral moment or heated exchange. Here are some data-driven approaches that can help cut through the noise:

First, ignore “instant polls” that ask questions only among people who watched the debate. That group is not likely to represent the feelings of the broader population. Instead, look for post-debate polls — (like ours with Ipsos and the Washington Post) — that ask questions among the same group of Americans both pre- and post-debate.

Second, in the days following the debate, look at data that captures attention to candidates, such as trends in search results or media coverage, to determine which candidate made the biggest splash. Media attention is crucial for candidates who aren’t well known to gain traction in the polls and with donors.

Finally, look for changes in horse-race polls in the week or two after the debate. There is a lot of noise in primary polls (especially this time around) and it can take some time for changes in public opinion to be reflected in our polling average.

The big thing to remember is that what’s important to journalists and television pundits may not be what’s important to the public, and we have to wait for pollsters to ask them how they feel.

-Analysis by G. Elliott Morris of FiveThirtyEight