Senate Republicans cited a rarely used point of order to silence Sen. Elizabeth Warren during a debate late Wednesday on the appointment of Alabama Sen. Jeff Sessions as attorney general. The Massachusetts Democrat was attempting to read out a decades-old letter from Coretta Scott King, Dr. Martin Luther King’s wife, that criticized Sessions as someone who “intimidated and frightened elderly black voters.”

Warren attempted to read the letter in the Senate as the House debated the appointment of Sessions to the Trump Cabinet. However, Republican Majority Leader Sen. Mitch McConnell, of Kentucky, invoked Rule XIX, saying Warren “impugned the motives” of Sessions and therefore was in violation of Senate rules.

The 10-page letter was sent in 1986 by Coretta Scott King to Strom Thurmond, then Judiciary Committee chair, urging him not to nominate Sessions as a federal judge. The letter was never entered into the congressional record but was published in January by the Washington Post.

King said that allowing Sessions to join the federal bench would “irreparably damage the work of my husband.” Sessions nomination failed in 1986, and Democrats have seized on the criticism of the time to attack his credibility as attorney general.

In his move to silence Warren, McConnell specifically referenced this sentence from the letter: “Mr. Sessions has used the awesome power of his office to chill the free exercise of the vote by black citizens.”

Warren is now barred from making any comment on the floor during the debate on Sessions appointment; a confirmation is expected sometime Wednesday.

Democrats quickly asserted the rule was not being applied consistently. Senate Minority Leader Chuck Schumer pointed to Sen. Ted Cruz’s accusation in 2015 that McConnell had told a “flat-out lie” about the future of the Export-Import Bank.

When she was unable to read the entire letter in the Senate, Warren turned to Facebook Live to read out the full text of a letter. At the time of writing the video has been watched more than 4.4 million times.

Several of Warren’s Democratic colleagues picked up the baton as the debate continued into the early hours of Wednesday, with Sens. Cory Booker and Jeff Merkley reading out sections of King’s letter, though stopping short of reading the specific excerpts that prompted the rebuke.

Soon after she was silenced, the hashtag #LetLizSpeak was trending on Twitter, with Warren herself using the social media platform to voice her opinions:

Warren also received the backing of her party. Interim chairwoman of the Democratic National Committee Donna Brazile said: “It’s a sad day in America when the words of Martin Luther King Jr.’s widow are not allowed on the floor of the United States Senate. Let Elizabeth Warren speak.”