WASHINGTON — During Donald Trump’s White House tenure, Republicans assembled the most conservative Supreme Court in a century. Now, they’re excited about the prospect of building on those efforts by confirming even more conservative justices, as well as lower-court judges, if he wins another four years.

GOP senators widely expect there would be at least one Supreme Court vacancy during a second Trump term — and in the event of the former president defeating Vice President Kamala Harris, Republicans would likely control the Senate, which handles the confirmation process. Two long-serving conservative justices will be on retirement watch in the coming years: Clarence Thomas, 76, and Samuel Alito, 74.

“High — extremely high to certain,” said Sen. Josh Hawley, R-Mo., who sits on the Judiciary Committee, when asked about the odds of Trump having the opportunity to appoint more Supreme Court justices if Republicans emerge victorious in the 2024 election.

“I think you’ll see, on the conservative side, at least one retirement. I’m speculating but I’m fairly confident of that,” Hawley said, adding that Republicans would probably look for more potential justices in the mold of Thomas and Alito — “particularly if we’re replacing one of those individuals.”

Sen. John Cornyn, R-Texas, who is running to be the next Senate GOP leader, said Trump’s first-term model for choosing young and conservative judges would likely continue, including for Supreme Court vacancies.

“I would think so. Obviously he worked with the Federal Society and other conservative legal organizations to come up with the best people and I thought he did an outstanding job with the Supreme Court,” Cornyn said.

If Trump were to get two more Supreme Court picks, he will have appointed over half the court, something no president has done since Franklin D. Roosevelt and the subsequent creation of the two-term limit.

“I don’t think any other president’s done that. That would be unprecedented,” Cornyn said. “The three we’ve confirmed has been a legacy, one of the best things the administration and President Trump did with a Republican majority. Five almost seems too much to hope for.”

Hawley added: “That could happen with Trump. It could. That would be big.”

For Democrats, that’s a scary possibility — and one they hope will motivate their voters to turn out this fall and prevent a Trump win.

“It would not be good,” Sen. Mazie Hirono, D-Hawaii, deadpanned.

“We would have even more getting rid of precedents. You’d have more Dobbs-like decisions. And there’s a whole slew of these kinds of decisions that the Supreme Court has been engaged in,” said Hirono, who serves on the Judiciary Committee. “It’ll just be worse. So I think what that will lead to is further calls, I hope, for Supreme Court reform.”

Neither Thomas nor Alito would be guaranteed to step down. But the two staunch conservatives might see the pairing of a GOP presidency and Senate control as an ideal opportunity to secure their legacies by keeping their seats in right-leaning hands for several more decades. It takes 51 votes to confirm a Supreme Court justice, so in that scenario Republicans would have the power to replace them without any input from Democrats.

The next oldest on the nation’s high court are liberal Justice Sonia Sotomayor, 70, and conservative Chief Justice John Roberts, 69.

On the campaign trail, Harris hasn’t said much about the prospect of Supreme Court vacancies under the next president. But she has repeatedly criticized Trump for picking the three justices who were essential to the five-member majority that overturned Roe v. Wade and ruled in a case involving Trump that presidents have immunity for official acts.

“So, so much is on the line in this election. … And this is not 2016 or 2020. It’s different for many reasons, but a very important reason among them is what the Supreme Court did just a few months ago,” Harris said at a recent fundraiser in Los Angeles. “The Supreme Court basically told the former president that he is effectively immune no matter what he does in the White House.”

Trump, who campaigned heavily on the Supreme Court in 2016, has said less about it this time as he finds himself on defense over his role in the overturning of federal abortion rights. His campaign did not respond when asked if he will release another list of high court prospects to choose from if he has another vacancy to fill.

Sen. Dick Durbin, D-Ill., the current chair of the Judiciary Committee, said Republicans would leap at the chance to fill another Supreme Court opening.

“They will move heaven and earth and defy all the precedents to fill the vacancy,” Durbin said in an interview, referring to the GOP-led Senate rushing through Justice Amy Coney Barrett days before the 2020 election.

He said that allowing Trump to appoint a majority of the Supreme Court would be a “desperate situation” — one that Democrats could do little to prevent if they lose the White House and Senate.

Mike Davis, the former chief counsel for nominations for Senate Judiciary Committee Republicans, said Trump’s judicial selections would be “even bolder” in a second term.

“President Trump’s biggest and most consequential accomplishment of his first term was his transformation of the Supreme Court to the first constitutionalist majority in 90 years,” Davis told NBC News, noting that Trump also tilted numerous powerful appeals courts to the right. “Trump will build on his success in his second term with his appointment of even bolder, more fearless federal judges.”

Sen. Thom Tillis, R-N.C., a center-right Republican on the Judiciary Committee, said he’s as “excited as you can be with the blood sport of SCOTUS nominations today” about “potentially having the opportunity to confirm another.”

“I’ve got four under my belt now, and I think that would be an exciting prospect for the country,” Tillis said. “I’m feeling pretty good about my support for all three of the Trump nominees.”