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Joe Biden limped into the South Carolina primaries in 2020.

He had finished fourth in Iowa, fifth in New Hampshire, and second — a distant second — in Nevada.

He needed South Carolina to stay alive, a state where 6 in 10 Democratic voters are Black. He needed Black people to save him.

During a debate just days before voting began in South Carolina, Biden made a promise to Black voters. Everyone is entitled to be treated with dignity, and everyone should be represented on the Supreme Court, he said: "I'm looking forward to making sure there's a Black woman on the Supreme Court, to make sure we in fact get every representation."

Black voters gave Biden the victory he needed, one that turned his campaign around and arguably set him on a path to win the nomination.

Now, with reports that Justice Stephen Breyer will retire in June or July, Biden has a chance to make good on his promise and repay Black people — at least on this measure — for their support.

This opening could not have come at a better time for Biden. He is struggling in the polls, unable to overcome Republican obstructionism and resistance from within his own party to deliver on several of the major promises he made to Black voters, such as passing federal police reforms and voter protections.

Poll after poll has pointed to growing dissatisfaction among Black voters.

Morning Consult data from October found that Biden's approval among Black voters was down 16 percentage points from the month before.

As NBC News reported in December: "Biden's approval among Black voters has been sliding throughout the year. A poll by HIT Strategies showed that 48% of Black voters said in November that Biden was addressing their needs, compared to 66% of respondents in June."

And as the Associated Press reported last week: "Just 6 in 10 Black Americans said they approved of Biden in a recent poll by The Associated Press-NORC Center for Public Affairs Research, down from about 9 in 10 who approved in polls conducted through the first six months of Biden's presidency."

The perception of Biden as a disappointment has been hardening among Black voters, the voters he needed to win in 2020 and the ones he would need again in 2024.

The Biden administration's attempts to turn things around have not borne fruit. This is not to say Biden hasn't had some big wins, particularly early in his term, but rather, that the losses loom large in recent memory, and they are continually piling up.

A Supreme Court opening offers Biden an opportunity to move beyond those losses, to change the conversation and the narrative, to emerge with a significant victory that he can hold up as proof of his success. It would put a major mark in the plus column.

No justice Biden nominates can change the ideological balance of the court significantly, but all new justices change the dynamic on the court. And every time an excluded group is included, that is good for the institution and its credibility.

It is important, I believe, that Black people have a Black person on the court more in tune with the views of the Black community than Clarence Thomas, the lone Black justice for the last 30 years. It has always struck me as a tragedy that Thomas was chosen to replace the liberal lion Thurgood Marshall.

Ideologically, it was like night and day, or night overtaking the day.

I remember knowing the name Thurgood Marshall for as long as I can recall knowing anything about the Supreme Court. As a child, I'm not sure I could have named another justice. As Biden suggested in South Carolina, representation matters — not just the skin of a person but also their soul.

Marshall's entire life was spent in the service of, and for the liberation of, Black people.

We need a justice who considers the Constitution in a clear-eyed way, as Marshall put it in 1987: "I do not believe that the meaning of the Constitution was forever 'fixed' at the Philadelphia Convention. Nor do I find the wisdom, foresight, and sense of justice exhibited by the Framers particularly profound. To the contrary, the government they devised was defective from the start, requiring several amendments, a civil war, and momentous social transformation to attain the system of constitutional government, and its respect for the individual freedoms and human rights, we hold as fundamental today."

I hope that little Black girls — and all children — can know the pride and sense of belonging I felt when I saw Marshall or said his name. I saw myself when I saw him. I believed that my voice was being heard because he was relaying it.

I also hope that young people will know, once again, what it feels like to have a person on the court who looks like them and can advocate for them and their positions, rather than being constantly confronted by the dissonance Thomas evokes.

Now is the time for a Black woman on the Supreme Court.

Charles M. Blow has been a New York Times Opinion columnist since 2008.