WASHINGTON — Setting up a high-stakes legal and political battle, President Trump said Monday he will announce his Supreme Court choice in a prime-time address Tuesday night, two days earlier than initially scheduled.

Trump did not disclose the identity of his nominee, but told reporters that his pick is “unbelievably highly respected” and people will be “very impressed” by the selection.

The scheduling announcement came via Trump’s Twitter feed: :I have made my decision on who I will nominate for The United States Supreme Court. It will be announced live on Tuesday at 8:00 P.M. (W.H.).”

Trump’s nominee will likely face intense opposition from Democrats in the Senate, where Republicans who hold a slim, 52-seat majority blocked former president Barack Obama’s choice of federal appeals court Judge Merrick Garland last year.

Trump made his scheduling announcement as he and aides continue to defend a new travel ban from seven Muslim countries, the subject of protests, lawsuits, and calls even by some Republican lawmakers to change the policy. The president had said last week he would name his Supreme Court nominee on Thursday.

In replacing the late Justice Antonin Scalia, the new president is selecting from a list of 21 people, nearly all of them federal or state judges, put together months ago by conservative interest groups. By last week, three favorites had emerged: federal appeals court judges Neil Gorsuch of Colorado, Thomas Hardiman of Pennsylvania and the original favorite, William Pryor of Alabama.

Democrats, led by Sen. Chuck Schumer of New York, have vowed revenge for what many consider a stolen Supreme Court seat. Unless Trump can win over eight of them, Republicans will have to change the Senate’s rules, eliminating the 60-vote threshold needed to bring the nomination to the floor. Trump endorsed such a move last week.

The goal for Trump, his aides and those groups has been to find someone in their 40s or early 50s with solidly conservative credentials who can serve on the Supreme Court for a quarter century or more. That makes the selection — and the Senate confirmation process — of more far-reaching importance than any of Trump’s nominees for his Cabinet or foreign postings.

Trump also had said he wanted a judge in the Scalia mold — one who follows the Constitution as written by the nation’s founders and federal laws as written by Congress, without imposing personal ideological or policy preferences.

While he can expect little cooperation from Democrats, Trump reached out to both sides last week, meeting with Senate leaders as well as the chairman and top Democrat on the Senate Judiciary Committee, which will conduct background checks and public hearings, most likely in March.

The White House is hoping to have the seat filled in time for the court’s April sitting, the last of the 2016 term, when several controversial cases could be considered involving such issues as religious liberty and transgender rights.

Some Democrats fear Trump wants to pack the high court with conservatives willing to roll back precedents on issues such as abortion, civil rights, environmental protection and government regulations.

Scalia’s death last Feb. 13 and President Obama’s effort to replace him with a moderate-to-liberal judge made the Supreme Court a prominent issue in the presidential election between Trump and Hillary Clinton. Conservatives — who risked losing control of the court for the first time in nearly 50 years — felt more strongly: Polls showed that among the one in five voters who said the court was their prime motivator, Trump was preferred by 57%.

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Replacing Scalia will not shift the court ideologically from where it was a year ago, but it will put conservatives one seat short of a commanding majority. With the seat filled, the longest-serving justice, Anthony Kennedy, once again will be the man in the middle — siding with conservatives in most cases but occasionally with liberals on issues such as abortion, affirmative action and gay rights.

But Democrats understand demographics. Kennedy, appointed by President Ronald Reagan in 1988, is 80 years old and considering retirement. President Bill Clinton’s two justices, Ruth Bader Ginsburg and Stephen Breyer, are 83 and 78, respectively.

One or more retirements would give Trump an opportunity to shift the court to the right, possibly for generations to come. Such shifts happen rarely, as when the moderate Justice Sandra Day O’Connor was replaced by the more conservative Samuel Alito in 2006, or when Justice Thurgood Marshall was replaced by Clarence Thomas a quarter century ago.

“The Supreme Court is what it’s all about,” Trump said in October’s last presidential debate. He vowed to name justices who “will not do damage to the Second Amendment” and allow decisions on abortion rights “to go back to the states.”

Scalia’s replacement won’t change the direction of the court initially. While it will remain in conservative hands — emboldening Chief Justice John Roberts and leaving Kennedy as the ultimate decider — the addition of a ninth justice will not cause a sudden move to strike down Supreme Court precedents such as those preserving abortion rights and the use of racial preferences. On campaign finance rules, gun rights and religious liberty, the court already leans to the right.

What could change in the short term is the court’s occasional willingness to step into disputes conservatives feel are better left to the states. That could spell doom for some of Obama’s forays into areas such as health care, immigration and environmental protection.

From the initial menu of 21 potential nominees — all judges except for Sen. Mike Lee, R-Utah — Trump whittled his list down to three in recent days:

• Neil Gorsuch, Colorado, U.S. Court of Appeals for the 10th Circuit. At 49 the youngest of the group, Gorsuch is the most natural replacement among them for Scalia. He is a strict adherent of originalism, Scalia’s belief that the Constitution should be interpreted based on the intent of the Founders. He also has much of Scalia’s flair as a writer.

Gorsuch has the type of academic credentials common to high court justices: Columbia, Harvard Law, even Oxford. He clerked for Justices Byron White and Anthony Kennedy, then practiced law in Washington and did a stint at the Justice Department.

• Thomas Hardiman, Pennsylvania, U.S. Court of Appeals for the 3rd Circuit. A dark horse among the finalists, Hardiman, 51, isn’t unfamiliar to Trump. He sits on the same U.S. Court of Appeals for the 3rd Circuit as the president’s sister, Maryanne Trump Barry, who recommended him.

Hardiman’s career as a judge is marked by law and order. He has maintained a solidly conservative record on issues involving guns, searches, police officers and prison guards — more so than Scalia, who often sided with criminal defendants against overzealous prosecutors. In that sense, Hardiman is much like Justice Samuel Alito, who came from the same appeals court.

• William Pryor, Alabama, U.S. Court of Appeals for the 11th Circuit. He’s been the conservatives’ justice-in-waiting for years, and at 54, the former Alabama attorney general comes straight out of central casting. Likely in his corner: U.S. attorney general-designate Jeff Sessions, who preceded Pryor as Alabama’s top law enforcement official.

But Pryor is controversial: He once criticized the Supreme Court’s 1973 decision in Roe v. Wade, which legalized abortion, as “the worst abomination of constitutional law in our history.” And he even has taken flack from conservatives concerned about a ruling he joined in favor of transgender rights.