Social media erupted over the weekend when news spread that U.S. Supreme Court Justice Ruth Bader Ginsburg won't be attending President Donald Trump's first State of the Union address Tuesday.

Some critics accused the 84-year-old justice of boycotting the president because of her publicly voiced distaste for Trump during the 2016 campaign, which she later said was “ill-advised.”

“Maybe she's house hunting in Canada?” was one tweet, a reminder that Ginsburg once hinted it might be time to move out of the United States if Trump was elected.

Others said justices had a duty to attend, no matter what they think of the president, while more than a few naysayers used the occasion to mock Ginsburg's penchant for nodding off during past State of the Union addresses.

“It's not fair that ppl are criticizing Justice Ginsberg for skipping SOTU!” former Arkansas Gov. Mike Huckabee tweeted, misspelling the justice's name as many people do. “Security concerns wouldn't allow her to bring CPAP machine into House chamber.” To illustrate his point, Huckabee included a 2015 photo (right) showing Ginsburg's head bowed while other justices listened attentively.

But the critics ignored two facts. Ginsburg nailed down two public appearances in Rhode Island for Tuesday long before the date of the State of the Union address was announced. And it is not uncommon for Supreme Court justices—liberal or conservative—to steer clear of the presidential address.

It was Aug. 31 of last year when Roger Williams University School of Law announced that Ginsburg would be on campus Tuesday for a public “fireside chat” with Bruce Selya, senior judge on the U.S. Court of Appeals for the First Circuit. Around the same time, she scheduled another event at a Providence synagogue for Tuesday night. It is typical for justices to arrange more than one event in the same area on the same day during out-of-town trips.

When she made the arrangements, she could not have known that Trump's State of the Union address would take place on the same day. As is customary, the date of the president's address before a joint session of Congress is worked out between the White House and the speaker of the House of Representatives. Speaker Paul Ryan first announced last Nov. 30 that Jan. 30 would be the day for Trump's talk.

No matter what the reason, Supreme Court justices have an uneven record of attendance at the State of the Union address. No justices at all showed up in 1975 and 2000. A possible factor is that both years came soon after cataclysmic political events; Richard Nixon's resignation in 1974 and Bill Clinton's impeachment trial in 1999.

For three years in a row in the early 2000s, according to a study of Supreme Court attendance, only one justice attended: Stephen Breyer, a political junkie who used to work in the Senate and thought it was important for all three branches of government to be on display. “In the State of the Union is the federal government, every part,” Breyer once explained. “The president, the Congress, the cabinet, the military, and I would like them to see the judges, too, because federal judges are also part of that government. And I want to be there.”

The late Justice Antonin Scalia quit attending in 1998, also according to the 2011 study by political scientists Todd Peppers and Michael Giles. Justice Samuel Alito Jr. has also mostly stayed away, complaining that justices have to behave like “potted plants,” careful not to applaud for anything political that the president says, for fear that clapping might be construed as an endorsement.

In 2010, Alito did attend and faced criticism for mouthing the words “not true” when President Barack Obama criticized the Supreme Court's Citizens United decision during the address.

The following year, Alito somehow found himself almost as far away from the State of the Union address as humanly possible. He served as jurist-in-residence at the University of Hawaii School of Law.