President Donald Trump is set on Monday night to announce his nominee for a lifetime position on the U.S. Supreme Court, with four conservative federal appellate judges as the top contenders to succeed retiring long-time Justice Anthony Kennedy.

The Republican president, with an opportunity to further put his stamp on the court with the second appointee of his 18 months in office, is expected to choose among four judges with strong conservative credentials: Thomas Hardiman, Brett Kavanaugh, Raymond Kethledge and Amy Coney Barrett.

All are young enough that they could serve on the nine-member high court for decades. Trump, who has touted Supreme Court nominations as among the most important task of his presidency, is poised to make his announcement at 9 p.m.

Trump is narrowing the field, with Barrett the least likely among the four to be chosen.

Hardiman, 53, has served on the Philadelphia-based 3rd U.S. Circuit Court of Appeals since 2007, having been appointed by Republican former President George W. Bush, after four years as a U.S. district judge in western Pennsylvania. Hardiman, a one-time cab driver from Waltham, Massachusetts who was the first member of his family to attend college, served alongside Trump’s older sister, Judge Maryanne Trump Barry, on the 3rd Circuit. She no longer hears cases.

Kavanaugh, 53, has served on the influential U.S. Court of Appeals for the District of Columbia Circuit since 2006. A former White House aide under Bush who previously worked for Kenneth Starr, the independent counsel who investigated Democratic former President Bill Clinton in the 1990s, he faced a long confirmation battle when Bush nominated him to his current post.

Kethledge, 51, has served on the Cincinnati-based 6th U.S. Circuit Court of Appeals since 2008 after also being appointed by Bush. A former aide to a Republican senator, Kethledge also previously worked as an in-house lawyer for Ford Motor Co.

Barrett, 46, has the least judicial experience of the four, with only eight months as a judge after spending most of her career as a conservative legal scholar. Barrett was appointed by Trump to the Chicago-based 7th U.S. Circuit Court of Appeals last year. Barrett, a married mother of seven and a devout Roman Catholic, is a favorite among social conservatives and conservative Christian leaders.