William Barr must make it through a hearing before the Senate Judiciary Committee Tuesday before he can become President Trump’s next attorney general.

This isn’t Barr’s first rodeo; the 68-year-old previously led the Department of Justice under the late President George H.W. Bush in the early 1990s.

Sen. Lindsey Graham, R-S.C., is the new leader of the Senate Judiciary Committee, which also includes multiple Democrats who are seen as potential 2020 contenders.

From their involvement in the confirmation hearing to questions Barr is sure to face regarding Special Counsel Robert Mueller’s investigation into Russian interference in the 2016 presidential election, here’s a look at five things to watch for in the hearing.

2020 contenders

Multiple Democrats thought to be potential 2020 presidential contenders sit on the Senate Judiciary Committee and could use the confirmation hearing to boost their national profiles, including Cory Booker, Kamala Harris and Amy Klobuchar.

During Supreme Court Justice Brett Kavanaugh’s contentious confirmation hearing last year, both Booker and Harris made headlines as they went on the offensive.

Booker even suggested he would be expelled from the Senate for defying a procedural norm by releasing “committee confidential emails.”

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And Harris openly suggested Kavanaugh was lying and hiding ties to Trump’s inner circle, though struggled to back up her assertion. She called the hearing a “sham” and “disgrace” and accused Kavanaugh of being anti-woman. That was before sexual misconduct allegations nearly derailed his confirmation.

Mueller investigation

Ahead of the hearing, Barr released prepared remarks in which he unequivocally stated he believes the Mueller probe should continue. As attorney general, Barr would oversee Mueller’s work.

“I believe it is in the best interest of everyone – the President, Congress, and most importantly, the American people – that this matter be resolved by allowing the Special Counsel to complete his work,” Barr said, according to the transcript. “The country needs a credible resolution of these issues. If confirmed, I will not permit partisan politics, personal interests, or any other improper consideration to interfere with this or any other investigation.”

He noted he’s known Mueller for three decades in a personal and professional capacity, calling him a “friend.” He has “confidence” that Mueller, who headed the Justice Department’s criminal division when Barr was previously attorney general, will “handle the matter properly,” according to the prepared remarks.

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Graham said he plans to question Barr over whether he would fire Mueller from leading the investigation.

“I’m going to ask him, ‘Do you see any reason to fire Mr. Mueller based on what you know now for cause?’” Graham told "Fox News Sunday" host Chris Wallace. “Do you trust Mr. Mueller to be fair to the president and the country?’ ‘Will you make sure he can finish his job?’ ‘If you get the report, will you be as transparent as possible?’ I’ve asked him those questions, and I’m very comfortable with his answers.”

Sen. Chris Coons, D-Del., told “Fox News Sunday” that he needs “a firm commitment” from Barr that he “wouldn’t allow any interference in the Mueller investigation – that he will allow it to reach its conclusion, and he will release his report to the public.”

Allegiance to Trump

Trump repeatedly decried former Attorney General Jeff Sessions, who recused himself from the Russia investigation, for not being loyal enough before he ultimately forced him from his Cabinet.

In his prepared remarks, Barr promised to “serve with the same independence” as he did during his first time in the job.

“At that time, when President George H.W. Bush chose me, he sought no promises and asked only that his Attorney General act with professionalism and integrity. Likewise, President Trump has sought no assurances, promises or commitments from me of any kind, either express or implied, and I have not given him any, other than that I would run the Department with professionalism and integrity,” Barr said. “As Attorney General, my allegiance will be to the rule of law, the Constitution, and the American people. That is how it should be. That is how it must be. And, if you confirm me, that is how it will be.”

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Democrats are likely to look at past instances where Barr’s view of presidential power could be relevant.

As deputy attorney general, Barr told Bush he did not need congressional approval to attack Iraq. Earlier, when he led the Justice Department's Office of Legal Counsel, he wrote opinions that allowed the U.S. government to invade Panama and arrest its dictator, Manuel Noriega, as well as to capture suspects without the consent of their host nations.

As attorney general in 1992, he endorsed Bush's pardons of Reagan administration officials in the Iran-Contra scandal.

Immigration amid shutdown

Barr’s confirmation hearing comes amid the longest partial government shutdown in U.S. history. Trump and Democrats remain at loggerheads over funding for a wall along the U.S.-Mexico border. Trump has demanded more than $5 billion for the wall, which Democrats have denied.

In his prepared remarks, Barr said the Justice Department should “continue to prioritize enforcing and improving our immigration laws.” He said it was vital to “secure our Nation’s borders, and we must ensure that our laws allow us to process, hold, and remove those who unlawfully enter.”

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In 1992, Barr pushed a multimillion-dollar plan for new fences and agents along the southern border. He said his proposal was a “steady march in the right direction,” albeit, not a “silver bullet” fix, The Washington Post reported at the time.

A border patrol chief told the newspaper then that the new fences didn’t “stop people,” but they did hinder people from driving cars or drugs across the border as well as block people from throwing rocks at agents. The fences gave “more control to a situation that had been out of control,” he said.

And as The Wall Street Journal reported, Barr attempted to rein in the asylum process, which he was critical of, during the Bush administration. He also oversaw a program which moved thousands of Haitian asylum seekers to Guantanamo Bay. The practice, which a critic called “the world’s first HIV detention camp,” was ended in 1993, according to CBS News.

Criminal justice

During his previous stint as attorney general, Barr advocated for an increase in prisons, penalties that are more severe and swift and laws to keep criminals behind bars longer.

However, he’s expected to tell lawmakers that he does, in fact, support the First Step Act, the recently passed, sweeping, bipartisan criminal justice reform legislation – even though he opposed a similar bill in 2015.

According to his prepared remarks, Barr will tell lawmakers that he will “diligently implement” the First Step Act, which he said “recognizes the progress we have made over the past three decades.”

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Still, Barr says the Justice Department must “keep up the pressure” on chronic and violent criminals.

Fox News’ Andrew O’Reilly, Gregg Re and The Associated Press contributed to this report.