After winning a 50-year fight to get Roe v. Wade overruled last year, the Republican Party faces tough questions on abortion access.

Should abortion be banned at conception or later? What exceptions should be allowed -- and if there are exceptions, how should that be enforced? Which medical emergencies would qualify? And should these decisions be made at the federal or state level?

For more on where the issue stands ahead of the first GOP primary debate, read here.

-ABC News' Anne Flaherty

Trump is snubbing the Republican National Committee and Fox News by counterprogramming the first GOP primary debate with an interview with Tucker Carlson.

Without the de facto GOP leader on stage, strategists are wondering how much the debate can shake up the race.

"For the trajectory of the entire primary, I don't think it matters that he's not there. I mean, probably no one remembers this debate after the next debate," said GOP strategist Rob Stutzman, a presidential campaign veteran.

Read more here.

-ABC News' Tal Axelrod

As several of the 2024 Republican presidential candidates are set to square off for the first time tonight, here are seven things to watch for during the debate.

-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

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