The Supreme Court this week will consider one of the biggest cases before it this term: a challenge to President Trump’s executive order restricting travel to the U.S. from eight countries that his administration has deemed to pose terrorism risks.

The justices will hear arguments in the case, Trump v. Hawaii, Wednesday, the last argument day for the justices this term.

Trump’s so-called “travel ban” has been the source of controversy, as the measure can be traced back to the campaign trail when then-candidate Trump vowed to ban Muslims from entering the U.S.

Since then, the president has tried three times to implement an executive order restricting travel to the U.S. from several Muslim-majority countries, only to face blockades by lower courts. But that could change, as the justices will finally wade into the controversy over the third version of the ban.

Issued in September, the president’s latest order suspended travel to the U.S. for foreign nationals from Chad, Iran, Libya, Somalia, Syria, Yemen, North Korea, and Venezuela. Trump dropped Chad from the list this month.

So far, the Trump administration hasn’t fared well in the lower courts. A federal judge in Hawaii blocked the executive order from taking effect last year, and the 9th U.S. Circuit Court of Appeals affirmed that ruling.

A similar case proceeded through the 4th U.S. Circuit Court of Appeals, which upheld a ruling from a federal judge in Maryland blocking the ban.

But the Supreme Court handed Trump a long-awaited victory in December when it allowed the order to take effect, and lifted the blockades from the federal judges in Hawaii and Maryland.

The justices then announced in January it would hear Hawaii’s challenge to the controversial measure on constitutional and statutory grounds. Legal watchers interpreted the unsigned order as a sign the Trump administration’s chance for victory had increased.

At issue in the case is whether Trump exceeded his authority under and violated federal immigration law by discriminating based on nationality. The justices will also examine whether Trump’s travel ban violated the Establishment Clause of the Constitution.

The Trump administration argues the Constitution and Congress have granted the president “broad authority” to place restrictions on the entry of immigrants to the U.S. when he believes it’s in the country’s interest.

Lawyers for the Justice Department said in their brief that the travel executive order was issued only after a “worldwide review” by government agencies that examined whether foreign governments provide adequate information to the U.S. that allows for proper vetting of foreign nationals.

The eight countries named in Trump’s proclamation, the administration says, “do not share adequate information with the United States" that would enable thorough vetting or present “other risk factors.”

But the parties challenging the travel ban, which includes the state of Hawaii and others, say the president’s proclamation seeks to ban more than 150 million immigrants from the U.S. solely on the basis of nationality. In doing so, the president has exceeded the authority delegated to him by Congress under federal immigration law.

But the Trump administration disagrees, and argues that based on these arguments, it would have been illegal for former Presidents Jimmy Carter and Ronald Reagan to place travel restrictions on foreign nationals from Iran and Cuba, respectively.

In addition to the statutory claims, the state of Hawaii argues the third iteration of Trump’s travel ban violates the Establishment Clause of the Constitution by essentially trying to ban Muslims.

“In short, an objective observer would still conclude that [the third executive order’s] purpose is the fulfillment of the president’s unconstitutional promise to enact a Muslim ban,” lawyers for the challengers wrote in a brief filed with the court.

A subsequent brief from the challengers cited Trump’s statements from the campaign trail extensively, including his formal statement in December 2015 calling for “a total and complete shutdown of Muslims entering the United States.” They assert Trump’s tweets and retweets demonstrate he was motivated by animus toward Islam, and say the inclusion of North Korea and Venezuela are "token restrictions" meant to disguise the move to target Muslims.

But Noel Francisco, the solicitor general, rejects the notion that Trump’s campaign statements can be used to form the basis for his reasoning for the travel ban.

“As the government has explained, those statements do not show that the proclamation rests on religious bias; indeed, they do not address the meaning of the proclamation at all,” Francisco wrote in a brief filed with the court this week.

The government also argues Trump’s statements in the campaign on Twitter are not relevant to the case.

“[T]he president’s retweets do not address the meaning of the proclamation at all,” Francisco wrote in the brief to the court.

While Trump’s remarks on the campaign trail could be a major flashpoint in arguments Wednesday, Josh Blackman, an associate professor at the South Texas College of Law in Houston, said he doesn’t believe the justices will give weight to those statements.

“I’m OK with courts looking at statements made by the president after the inauguration. I think the campaign trail has to be off limits,” he said during a call with reporters Friday. “There’s certain chilling repercussions if courts start quoting candidates.”

Blackman predicted that if the court says campaign statements are relevant, Trump is likely to lose. But he warned that if the justices rule against the administration and “give a green-light for courts to parse campaign statements and the like, this could potentially hamstring not just this president but also future presidents.”

Ilya Somin, a law professor at George Mason University, argues that the Supreme Court’s pre-textual jurisprudence has indicated evidence of the historical background of a decision is allowed.

“You can look at the specific sequence of events leading up to the challenged decision,” he said during the call. “I think it’s obvious that Trump’s campaign promises are part of that specific sequence of events and that absent that sequence, you would never have seen anything like this travel ban policy or even remotely similar to it.”

Contrary to Blackman, Somin warned that upholding the travel ban would prove to have negative consequences.

“If this is upheld, it creates a roadmap for future presidents and by the way other politicians to enact bigoted policies, if you say what you’re truly going to do on the campaign trail and use more modest rhetoric after you get elected,” he said.

The travel ban case has attracted a wide variety of friend-of-the-court briefs, with more than 70 submitted to the Supreme Court from parties ranging from universities and law enforcement officials, to Khizr Khan, the Gold Star father who addressed the Democratic National Convention, and the children of Fred Korematsu, a Japanese American who challenged President Franklin D. Roosevelt’s executive order calling for the internment of Japanese Americans on the West Coast during World War II.

The Supreme Court upheld Roosevelt’s order in what has since become a highly criticized decision.

A decision from the court in the travel ban case is expected by the end of June.