Former Vice President Joe Biden reiterated his pledge at Sunday night’s debate to appoint a black woman to the Supreme Court.

Only two African Americans, Justices Thurgood Marshall and Clarence Thomas, have served on the Supreme Court. And only one woman of color, Justice Sonia Sotomayor, has joined the Court. If Biden is elected and follows through on that promise, his nominee would be the first black woman to serve as a justice.

The identity of that nominee could depend on how soon a vacancy opens up on the Supreme Court — if the vacancy occurs relatively late in a Biden presidency, the former vice president would have more time to fill the lower courts with potential candidates for a Supreme Court appointment.

If a seat were to open up on the Supreme Court early, one obvious contender for such a nomination is Judge Ketanji Brown Jackson, who currently serves on the US District Court for the District of Columbia.

Judge Jackson, who is only 49 years old, clerked for Justice Stephen Breyer. She was also one of a handful of judges who President Obama interviewed for the Supreme Court vacancy opened up by Justice Antonin Scalia’s death in 2016. Obama eventually nominated federal appellate Judge Merrick Garland, who was blocked by a Republican Senate.

Another relatively youthful potential nominee is Justice Leondra Kruger, a 43-year-old former law clerk to Justice John Paul Stevens, who currently sits on the California Supreme Court.

The progressive advocacy group Demand Justice also published a list of potential Supreme Court nominees which includes several African American women, including Kruger, criminal justice scholar Michelle Alexander, NAACP Legal Defense Fund president Sherrilyn Ifill, and New York University law professor Melissa Murray.

Of course, for Biden to follow through on this pledge, he will need to secure the nomination, win the presidency, wait for a vacancy, and then get that nominee through the Senate — something that may be impossible if Republicans retain a Senate majority.