Justice Anthony M. Kennedy announced his resignation from the Supreme Court on Wednesday, launching what promises to be an all-out partisan brawl in the Senate over the confirmation of President Donald Trump’s choice to quickly fill the vacancy.

Kennedy, 81, spent the last of his three decades on the Supreme Court as the deciding vote on many of the court’s most contentious cases. Although conservative, he sometimes joined the liberal wing of the court and authored landmark opinions on cases dealing with abortion, campaign finance and LGBT rights, including same-sex marriage.

Kennedy’s departure from that influential role means a second Trump appointment — expected to be more consistently conservative than Kennedy — would shift the Supreme Court further to the political right and solidify that conservative tilt for years.

“It has been the greatest honor and privilege to serve our nation in the federal judiciary for 43 years, 30 of those years on the Supreme Court,” Kennedy said through the court’s press office.

Kennedy told his colleagues he would submit a letter to Trump, according to the press office. The office also said “that while his family was willing for him to continue to serve, his decision to step aside was based on his deep desire to spend more time with them. He said, too, that admiration for his colleagues on the Court means that he will retain warm ties with each of them in the years to come.”

Watch: McConnell Vows Vote on Kennedy Successor ‘This Fall’

Majority Leader Mitch McConnell said on the Senate floor that a confirmation vote would be held this fall. Trump said his search for a Supreme Court nominee will “begin immediately” and he intends to make his selection from a list of more than 20 reliably conservative candidates the White House released last year. Both conservative and liberal interest groups are poised to press the fight.

“During his tenure on the Court, he authored landmark opinions in every significant area of constitutional law, most notably on equal protection under the law, the separation of powers, and the First Amendment’s guarantees of freedom of speech and religion,” the White House said in a statement.

Legal experts and lawmakers predict that Kennedy’s departure could mean major changes in the nation’s legal landscape when it comes to civil rights, environmental enforcement, voting rights, and particularly the protections flowing from Roe v. Wade, the landmark 1973 decision that legalized abortion.

“It would mean we have a new legal order,” said Josh Blackman, a professor at the South Texas College of Law in Houston who closely follows the court. “For the past three decades or so, Justice Kennedy has been at the center of every major legal dispute to come to the court, and now that’s no longer the case.”

Chief Justice John G. Roberts Jr., a conservative George W. Bush appointee, could become the center of the court, Blackman said.

And it will only add to the political magnitude of the nomination at a time when Washington seems to zoom from crisis to crisis about trade and tariffs, foreign relations and immigration enforcement.

Senate Judiciary Chairman Charles E. Grassley of Iowa has also signaled he will press for a quick confirmation process this year.

A confirmation hearing usually happens about two months after a nomination is announced. “I’d like to have it announced right away so we can get to work on it,” Grassley said.

But Senate Democrats still harbor a retributive impulse toward McConnell and the Republicans, who blocked the nomination of U.S. Circuit Judge Merrick Garland, President Barack Obama’s pick to fill the seat of the late conservative Justice Antonin Scalia.

Watch: Schumer Says Supreme Court Vacancy Shouldn’t Be Considered in Election Year

“If a vacancy occurs during this term, after the Garland heist, the balance of the court could be tilted even more against women’s, workers’, and civil rights for decades to come by the president’s list of 25 judges who have passed his litmus test of overturning Roe v. Wade,” Democratic Sen. Kirsten Gillibrand of New York wrote Tuesday on Twitter.

Yet Democrats are powerless to stop a Trump nominee without help from Republicans, since it only takes a majority vote to navigate the procedural hurdles in the confirmation process. McConnell changed rules for filibusters on Supreme Court justices last year to overcome Democratic opposition and confirm Trump’s first appointment, Justice Neil Gorsuch.

“I don’t think they could put up a bigger one than they did against Gorsuch,” Grassley told CQ on Tuesday of the possible Democratic fight over the nomination. “The White House has to be cognizant of the fact they want to nominate someone who’s going to get all 51 Republican votes.”

Leonard Leo, an outside advisor to Trump on judicial nominations who is on leave from his post at the Federalist Society, said Trump’s list of potential nominees for this vacancy includes many of the very best judges in America.

“I expect the nominee to be like Justice Gorsuch, to demonstrate excellence in every respect, and to earn widespread support from the American people, and bipartisan support for confirmation in the Senate,” Leo said.

The confirmation machinery would gear up quickly. Grassley said the Senate could provide the extra funds for additional committee majority and minority staff, and he would want the nomination right away.

McConnell already said in May that a potential Supreme Court battle would move to the front of the judicial confirmation pipeline. “If there is a Supreme Court vacancy, it takes priority. No question about it,” McConnell said.

Majority Whip John Cornyn of Texas a member of the Senate Judiciary Committee, told reporters Wednesday that Democrats can’t block the nominee.

“There used not to be filibusters of judges until the George W. Bush presidency, and now all the filibuster activity and precedents have been overruled, so we are looking at 51 to confirm or 50 plus the vice president,” Cornyn said. “I’m optimistic we’ll be able to get this done.”

Democratic Sen. Richard Blumenthal told reporters that members of his party will have a voice and a vote.

“We will be looking at the qualifications, the personal background of any nominee,” Blumenthal said. “That research will be immensely important, and so will be the questions that we ask, as they were with Justice Gorsuch, even though we disagreed with the result.”

The thing lawmakers from both sides agreed on Wednesday is that the stakes are incredibly high.

“People should understand that this nominee will be there for decades to come, for our lifetimes and a good part of our children’s lives,” said Blumenthal, a Judiciary Committee member. “And the consequences for our nation couldn’t be higher.”

Michael Waldman, president of the Brennan Center for Justice at NYU School of Law, said Kennedy’s role as the deciding votes in big cases means this confirmation fight will be more consequential than any in decades.

“This will be one of the great constitutional fights of the country’s history,” Waldman said. “No nominee should be rammed through without due consideration and debate. The seat should not be filled with someone who threatens or undermines voting rights, individual freedoms, or the balance of powers enshrined in our founding documents.”

Jeremy Dillon and Ryan McCrimmon contributed to this report.