President Donald Trump will soon have the opportunity to nominate a new Supreme Court justice after Justice Anthony Kennedy announced his retirement Wednesday.

Dr. Michael Slobodchikoff, chair of the political science department at Troy University, said the opportunity for Trump to replace a justice known for being the “swing vote” is a momentous occasion that will shape the political sphere for years to come.

“It’s fairly rare that in a person’s first two years that they have a chance to nominate two Supreme Court justices,” Slobodchikoff said. “The first nomination to replace justice Antonin Scalia didn’t change the makeup of the court at all but Kennedy was a swing vote. This will be a big deal because the makeup of the court will change.”

The 81-year-old Kennedy, often a voice of moderation over three decades on the court, provided the key vote on such closely divided issues as affirmative action, guns, campaign finance and voting rights in addition to same-sex marriage and the right to abortion.

“On things like gay marriage and more social issues, he often voted with left-leaning justices,” Slobodchikoff said. “On other issues, he sided with conservative justices. This gave him a lot of power on the Supreme Court. You could not win a court case unless you convinced him to side with you.”

The other eight members of the court during Kennedy’s term were historically evenly split with four conservative-leaning justices and four liberal leaning justices.

Trump already replaced one Supreme Court justice in his term, nominating Neil Gorsuch to replace Scalia, although Scalia passed before Trump was elected.

“Scalia died in (Barack) Obama’s last year before the election,” Slobodchikoff said. “Mitch McConnell, majority leader in the Senate, refused to have a hearing on Obama’s replacement for Scalia. We had to wait until after the election, which gave Donald Trump the ability to nominate Gorsuch.”

McConnell did not allow a vote on Obama’s nomination, Merrick Garland, before the election, something that some Democrats have pointed out since Kennedy announced his retirement, stating that the midterm elections should be held before a nomination is made so that the voters have a chance to change the makeup of the Senate and potentially vote in a Democratic majority.

Slobodchikoff said he does not expect McConnell to wait for the midterm elections.

“McConnell wants to have this nomination as soon as possible,” Slobodchikoff said.

He added that even if the nomination were to be held after the midterm elections, Democrats are not guaranteed to gain a majority in the Senate.

Because of rule changes made by McConnell during the nomination of Gorsuch, Slobodchikoff said Democrats will have few options to block a conservative candidate for the seat.

“There is no way the Democrats can filibuster a Supreme Court justice any more with the way the rules were changed when Gorsuch was nominated,” Slobodchikoff said. “It would now take only a simple majority vote. Currently, Republicans have a one-vote majority in the Senate. (Senator John) McCain is sick with cancer though and probably would not be able to vote currently, so it could be a 50/50 split. But in that case, the deciding vote would go to (Vice President) Mike Pence.”

Slobodchikoff said the nomination of a conservative justice will likely bring major changes to the legal landscape in America.

“Take for example the Supreme Court’s recent vote on Trump’s travel ban – they declared it constitutional,” Slobodchikoff said. “The separation of families at the border is going to make it’s way to court, gay marriage, abortion … We’ll probably see a rollback in gay rights and abortion rights.”

No matter who is elected president in the next term, Slobodchikoff said the new makeup of the Supreme Court could last for decades.

“Supreme court justices are nominated for life,” Slobodchikoff said. “If President Trump nominates someone young enough in his or her 60s, that person could easily be on the court for the next 20-25 years.”

And Trump may have even more opportunities to stack conservative justices on the court. The two oldest justices on the court are liberal judges Ruth Bader Ginsburg, 85, and Stephen Breyer, 80.

“You know, you’ve always got to worry about age as an issue on the Supreme Court,” Ginsburg said. “Justice Ginsburg is one of the oldest members of the Supreme Court. She is healthy currently, but age is a huge factor … My guess is that Ginsburg wants to retire during a Democratic presidency if she can.”

Slobodchikoff said that if the nomination were to be held after the mid-term elections and the Democrats did retake control of the Senate, Trump would still make the nomination, but it would need more bipartisan support, meaning the candidate would likely be more akin to the swing-voting nature of Kennedy.

Another possibility for the Democrats is to convince one or two moderate Republican Senators to block a solidly conservative candidate based on some of those potential threats to abortion rights, for instance.