Justice Sonia Sotomayor will not participate in one of the two cases the Supreme Court will hear in April to decide whether the Constitution forbids states from dictating how members of the electoral college cast their votes for president.

The clerk of the court informed lawyers in the case Tuesday that Sotomayor realized she is friends with one of the parties in one of the cases, from Colorado. Sotomayor will still participate in the other case, from the state of Washington.

“The justice believes that her impartiality might reasonably be questioned due to her friendship with respondent Polly Baca,” Supreme Court Clerk Scott S. Harris wrote. “The initial conflict check conducted in Justice Sotomayor’s Chambers did not identify this potential conflict.”

That is somewhat surprising. According to news reports, Baca and Sotomayor consider each other old family friends, and Baca attended Sotomayor’s confirmation hearing. According to an article in the Denver Post, Baca organized a gathering in Denver to watch the confirmation vote, and Sotomayor joined them via speakerphone.

“Polly, you know how much I love you, and how much I love your senators, who both voted for me,” Sotomayor said, according to the report.

Justices decide for themselves whether to recuse from a case, even though President Trump recently called on Sotomayor and Justice Ruth Bader Ginsburg to recuse from anything “Trump-related” that came before the court. Neither responded, and this case is not one that could provide an obvious partisan advantage.

It is rare but not unheard of for a justice to realize after a case has been accepted that there is a personal connection or that the justice was involved in the case previously.

In the electors case, Polly Baca is a party, but it is another elector, Michael Baca, who has received the most attention. (Michael Baca says the two are not related.)

While Polly Baca and another elector, Robert Nemanich, challenged Colorado’s requirement that electors vote for the winner of the statewide vote — in 2016, it was Hillary Clinton — both eventually voted for her.

Michael Baca attempted to vote for Republican John Kasich, as part of an effort to deny the presidency to Trump by electing a compromise Republican. Michael Baca was replaced by an alternate after a court ruled that the state’s electors were required by law to vote for the candidate who won Colorado’s vote.

The U.S. Court of Appeals for the 10th Circuit eventually ruled against Colorado.

The Supreme Court has never fully addressed whether states may punish or replace “faithless” presidential electors who refuse to support the winner of their state’s popular vote.

Lower courts have split on the question, and both red and blue states urged the justices to settle the matter in advance of the “white hot” glare of the 2020 election. They say they fear a handful of independent-minded members of the electoral college deciding the next president.

The federal appeals court said electors were free to vote as they choose.

“While the Constitution grants the states plenary power to appoint their electors, it does not provide the states the power to interfere once voting begins, to remove an elector, to direct the other electors to disregard the removed elector’s vote or to appoint a new elector to cast a replacement vote,” wrote Judge Carolyn B. McHugh.

In the 2016 election, 10 electors attempted to freelance and vote for someone other than Clinton or Trump.

In the Washington case, a majority of the state Supreme Court said the Constitution “explicitly confers broad authority on the states to dictate the manner and mode of appointing presidential electors.” Additionally, nothing in the document “suggests that electors have discretion to cast their votes without limitation or restriction by the state legislature.”

It ruled against three electors who voted for former secretary of state Colin Powell instead of Clinton, and upheld the Washington law requiring electors to support their nominee of their party or be subject to a civil fine of up to $1,000.

The cases are Chiafalo v. State of Washington and Colorado Department of State v. Baca.