Republican debate highlights and analysis: Fiery faceoff on Trump, Ukraine and more

Burgum’s debate appearance was in doubt after he suffered an injury while playing pick-up basketball with his staff.

Just hours before the start time, he announced he’ll be on stage after all.

His team is already fundraising off the incident, selling T-shirts with a silhouette of a cowboy hat-clad Burgum playing basketball -- a twist on the famous Nike Air Jordan "Jumpman" logo.

Earlier in the day, the governor was visibly emotional as he discussed the pain he was feeling with ABC News.

"I'm someone who's never taken prescription pain meds and I'm not doing that today. Even though people said that'd be a good idea. Because I’d rather … I mean so many Americans make so many sacrifices, think law enforcement, think of military, what they do for all of us," he said.

"I mean, if you're gonna lead this country, you got to be able to stand on one leg for two hours. You know, it's not, it's not 'Dancing with the Stars.'"

-ABC News' Alexandra Hutzler and Oren Oppenheim

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