Republicans will hold their first debate of the 2016 presidential campaign on Thursday in Cleveland, Ohio. The crowded 17-candidate field prompted debate host Fox News to divide the field into two — a primetime showdown featuring the top ten highest polling candidates at 9 p.m., and a 5 p.m. debate for the other seven. Here are six things to watch for during the main event, and one key question about the earlier debate:

1. How will the moderators and other candidates deal with Donald Trump?

Trump has become the story of the 2016 Republican race. Polls show him leading the field, although surveys this early in a race are rarely predictive of the eventual winner. He is the most colorful Republican candidate, even if Trump is probably not a viable nominee for the party.

The moderators, Fox News’ Bret Baier, Megyn Kelly and Chris Wallace, face a number of challenges in dealing with Trump, a master at both self-promotion and message control. How do they pin down Trump on policy issues and get him to acknowledge that some his ideas are unrealistic, such as getting the Mexican government to pay for the creation of a wall that would cover the entire U.S.-Mexican border? Can they force Trump to be specific, instead of offering one-liners, like his promise to replace the Affordable Care Act with “something terrific?”

And how will they ask Trump about his controversial remarks, such as suggesting that the Mexican government is intentionally sending rapists to the U.S.?

In his two months as a candidate, Trump has repeatedly mocked his rivals, particularly former Florida Gov. Jeb Bush. This also creates a dilemma for the moderators.

Trump is the kind of candidate who could attack a couple of rivals and turn the debate into a shouting match in which is shaping the dialogue, with most of the other nine candidates left watching. With only two hours and 10 candidates, the debate moderators will be trying to avoid this becoming the Trump Show.

They may not succeed.

2. Will the other candidates attack Trump or Jeb Bush?

Trump leads in the polls, but much of the Republican establishment is behind Bush. Most party operatives believe the former Florida governor, not Trump, is more likely to win the nomination.

It’s still early in the process, with the Iowa caucuses not scheduled until February. So the other candidates may have little incentive to attack anyone at this stage, and instead use this debate to introduce themselves to the broader electorate.

On the other hand, victory for the more moderate Republicans in the race, such as Ohio Gov. John Kasich and Florida Sen. Marco Rubio, will likely require Bush faltering.

So do these candidates start taking digs at Bush?

For the more conservative candidates, such as former Arkansas Gov. Mike Huckabee, taking on Bush may have some benefits as well. They could link Bush with President Obama and Hillary Clinton, arguing all three support “amnesty” for illegal immigrants. Becoming the chief anti-Bush candidate would be valuable to the campaigns of Huckabee or Texas Sen. Ted Cruz.

Don’t expect Huckabee or Cruz to attack Trump. They are assuming Trump will decline at some point because of his bombastic style and lack of political experience, and that they can win his voters without taking on Trump directly.

Instead of attacking the mogul, Cruz and Huckabee have ramped up their rhetoric against President Obama and Hillary Clinton to Trump-like levels, mostly notably when Huckabee suggested the Iran nuclear deal could lead to a second holocaust of Jewish people.

3. Will Bush Be Pressed on Any Of His More Moderate Stands?

Bush has made it a hallmark of his campaign that he will not move sharply to the right on key issues, particularly immigration.

So he may have to grapple with questions about his support for creating a path to legalization for the estimated 11 million undocumented immigrants and his past support for the Common Core education standard.

4. Can Wisconsin Gov. Scott Walker, Kasich or Rubio Live Up to the Hype?

Kasich, Rubio and Walker are generally considered the strongest potential challengers to Bush, with their records of winning in key swing states and potential appeal to all wings of the GOP. But Rubio has not surged in the polls or consolidated those in the party’s establishment who are wary of a third Bush presidency.

Walker has at times given short, clipped answers to questions that have raised doubts about his policy knowledge. He is the candidate with perhaps the most to lose in these debates, particularly if he has a moment that reinforces concerns about his smarts. The debates severely weakened the candidacy of then-Texas Gov. Rick Perry in 2011.

5. Will any new policy differences emerge between the candidates, or will this be a session of Obama-Clinton bashing?

The Republican candidates have already had forums all over the country. Beyond immigration, few policy differences have emerged. The candidates are often content to criticize Obamacare, the nuclear agreement the Obama administration reached with Iran and the various controversies surrounding Clinton. They often use very similar talking points in attacking the president and former secretary of state.

And the GOP candidates have offered few detailed proposals on what they would do if elected president.

6. Can neurosurgeon Ben Carson, New Jersey Gov. Chris Christie or Kentucky Sen. Rand Paul bring any attention to themselves?

This trio looks politically dead. Christie and Paul, who seemed like rising stars in the GOP in 2013 and 2014, are struggling as candidates, getting little support from party activists or the Republican establishment. And Carson, who was always a long-shot to win, has been eclipsed by Trump as the straight-talking non-politician beloved by very conservative voters.

7. Are any of the candidates not on the debate stage viable?

Probably not. Former Virginia Gov. Jim Gilmore, ex-HP CEO Carly Fiorina, South Carolina Sen. Lindsey Graham, Louisiana Gov. Bobby Jindal, former New York Gov. George Pataki, former Pennsylvania senator Rick Santorum and Perry didn’t finish in the top 10 in polls, so they didn’t qualify for this debate. Other networks are using different criteria, so they could participate in debates in the future.

The reality is that these candidates not qualifying for the debate is a symptom of other problems with their candidacies. There was never much eagerness in the Republican Party for presidential campaigns from Gilmore, Fiorina, Graham, Jindal or Pataki.

Perry and Santorum ran in 2012 and lost, and the Republican Party had already given signs these two would not get a second chance. Many supporters, donors and aides to Perry and Santorum four years ago are now aligned with other candidates.