Trump maintains a lead of 25 percentage points over his nearest competitor in Iowa, according to the latest polls.

DeSantis and Scott are both polling higher in Iowa than they are nationally, according to our polling average. Trump is polling about 10 points lower in Iowa than in national polls.

According to a July poll from J.L. Partners/DailyMail.com, only 51 percent of Iowa Republicans said their mind was made up. Forty-three percent said they could still be persuaded to support another candidate. Voters who said they plan to vote for Trump were the most likely to say their mind is made up, with 80 percent saying so compared with 37 percent of those who said they plan to vote for DeSantis and 11 percent of those who said they plan to vote for Scott.

Scott and DeSantis have the highest net favorability among Iowa Republican voters. Pence, Christie and Hutchinson are underwater.

In an early state poll from the Manhattan Institute conducted in July, Iowa Republicans are split on whether electability is important. Forty-six percent of Iowa Republican voters say that it is most important for Republican candidates to win elections and be in power, even if that means compromising or moderating their positions, while 45 percent said it is most important for candidates to stay true to their principles, even if that means losing elections.

Iowa Republicans also think that skipping primary debates shows weakness more than strength, according to a July Fox Business/Beacon Research/Shaw & Co. Research survey. Fifty-nine percent of Republicans said skipping the debate shows weakness, while 27 percent said it shows strength.

-Analysis by FiveThirtyEight

If you’re trying to gauge which Republican primary candidate would perform best against Biden in next year’s general election — their “electability” — their favorability ratings are a helpful signal. According to FiveThirtyEight’s polling averages, Biden is viewed favorably by 41.6 percent of U.S. adults and unfavorably by 53.9 percent, for a net rating of -12.3 percentage points. That compares to a net favorability rating for Trump of -16.5 points (39.7 percent favorable and 56.2 percent unfavorable). Given those numbers, a reasonable observer might expect Biden to beat Trump in the popular vote in 2024, all else being equal. (Of course, it never is).

Many of the other candidates — like Ramaswamy and Scott — have higher net favorability than Biden. But that doesn’t mean they’d actually perform better against the incumbent president in a general election. Candidates’ net favorability tends to decline as more people know them. To get a sense of how popular some of the less-known candidates are, we can use a regression model to quantify the relationship between name recognition and net favorability and then estimate what each candidate’s net favorability rating should be based on how many people know them. Then, we can compare the actual number to that benchmark and get a better sense of who is overperforming or underperforming. On this metric, Scott and Ramaswamy score the best of the non-Trump field, with current net ratings that are 5 and 6 percentage points, respectively, higher than we would predict for them. Christie, meanwhile, trails the field with a net favorability rating 15 percentage points lower than his benchmark.

-Analysis by G. Elliott Morris of FiveThirtyEight

The Republican National Committee will release an ad during the debate Wednesday night promoting early voting -- a method that some in the GOP acknowledge they have fallen behind on in recent years.

Included in the ad are RNC Chairwoman Ronna McDaniel, former Vice President Pence and former President Trump, who promotes the party's new early voting effort launched earlier this year.

The party is also planning to have a Bank Your Vote booth in Milwaukee on Wednesday, with absentee ballot request forms from all 56 states and territories.

The GOP has struggled to regain parity with Democrats on early voting after Trump baselessly lambasted the method as ripe for widespread fraud, without providing evidence for his claims.

-ABC News' Tal Axelrod

President Joe Biden's reelection campaign was noncommittal Wednesday when asked if he would debate the ultimate GOP presidential nominee.

"We have not had a conversation about that at all," Biden campaign co-chair Cedric Richmond told reporters during a press conference Wednesday. "I'm sure one day we will. But it's not today and I don't have any news on that. But what we're going to continue to do is continue to govern because Vice President [Kamala] Harris and President Biden have a job to do and they take it serious. So when we have news on that, we’ll let you know."

Biden and his allies have gone after the entire Republican primary field, tying them all to the "MAGA" brand of former President Trump.

However, the future of presidential general election debates is up in the air after the Republican National Committee last year voted to quit the Commission on Presidential Debates, the non-partisan group that has put on general election debates since 1988.

Biden's campaign also defended its decision to not engage in any Democratic primary debates, boasting that the president, as the incumbent, is the presumed nominee despite facing challenges from Robert F. Kennedy Jr. and Marianne Williamson.

-ABC News' Tal Axelrod

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