Senate Republicans turned to an arcane rule to silence Democratic Sen. Elizabeth Warren on the Senate floor Tuesday for criticizing colleague and attorney general nominee Jeff Sessions with the words of Coretta Scott King from 30 years ago.

The wife of Martin Luther King Jr., and civil rights leader wrote in a letter that Sessions, as an acting federal prosecutor in Alabama, used his power to “chill the free exercise of the vote by black citizens.” The letter aided in the 1986 voting down of then-nominee Sessions to be a federal court judge.

Warren resurrected the letter in hopes of preventing the Alabama Republican with a sketchy civil rights record from being confirmed as the next Attorney General under President Donald Trump. The letter was written 10 years before Sessions was even elected to the Senate.

But Warren was instead stunned by being given a rare Senate rebuke for impugning a fellow senator, and was barred from saying anything more on the Senate floor about the nominee.

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She had been warned to be aware of the rule, and then later was interrupted by Senate Majority Leader Mitch McConnell who said she had “impugned the motives and conduct of our colleague from Alabama.”

Quoting King technically put Warren, the Massachusetts senator, in violation of Rule 19, which states, in part: “No Senator in debate shall, directly or indirectly, by any form of words impute to another Senator or to other Senators any conduct or motive unworthy or unbecoming a Senator.”

Warren was appalled.

“I am surprised that the words of Coretta Scott King are not suitable for debate in the United States Senate,” she said. “I ask leave of the Senate to continue my remarks.”

She added: “I’m reading a letter from Coretta Scott King to the Judiciary Committee from 1986 that was admitted into the record. I’m simply reading what she wrote about what the nomination of Jeff Sessions to be a federal court judge meant and what it would mean in history for her.”

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Warren then jumped on her Twitter account to denounce the proceedings.

Democrats quickly came to the defense of Warren with rebukes of the Republicans in the Senate on Twitter using the hashtag #LetLizSpeak.

On the other side, Republican Sen. Orrin Hatch tweeted out Rule 19.

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Warren is silenced for reading old letter by MLK’s wife opposing Sessions and then all hell breaks loose Senate TV via AP