Senate Republicans voted on Tuesday night to silence Massachusetts senator Elizabeth Warren, who had taken to the floor of the Senate to give a speech opposing the confirmation of Alabama senator Jeff Sessions as attorney general. Warren began reading a letter written in 1986 by the late Coretta Scott King, activist and wife of civil-rights leader Dr. Martin Luther King Jr., which was originally written in opposition to Sessions’s 1986 nomination to serve as a federal judge. (King’s letter was written to be sent to the Senate, though Senator Strom Thurmond, who was then the chair of the judiciary committee, blocked it from being entered into the congressional record.) In her letter, King wrote, “Mr. Sessions has used the awesome powers of his office in a shabby attempt to intimidate and frighten elderly black voters. For this reprehensible conduct, he should not be rewarded with a federal judgeship.” (Sessions’s nomination for the judicial post was ultimately withdrawn amid allegations of past racist comments, some of which he has denied.)

But Republicans immediately took offense to Warren reading King’s words on the Senate floor. Senator Steve Daines of Montana warned Warren that she was violating Senate rules against impugning another senator. She continued reading King’s letter anyway. “Mrs. King's views and words ring true today,” Warren said. “The integrity of our Justice Department depends on an attorney general who will fight for the rights of all people. An honest evaluation of Jeff Sessions’ record shows that he is not that person.” Civil-rights advocates and lawmakers have expressed concern over Sessions’s record on race and immigration, as well as statements he’s made in the past. Sessions has been criticized for calling the N.A.A.C.P. “communist-inspired” and “un-American,” and for allegedly calling a black assistant U.S. attorney “boy.”

Warren’s speech came to a halt when Senate Majority Leader Mitch McConnell invoked rule XIX, which keeps senators from “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, McConnell said, “has impugned the motives and conduct of our colleague from Alabama.”

Warren remarked that she was “surprised” that reading King’s letter would be considered inappropriate, and asked for permission to continue, which McConnell denied. Warren appealed, but the Republican-controlled Senate voted 49–43 to uphold a ruling that Warren had violated Senate rules. Now, Warren is barred from speaking until the fight over Sessions’s nomination ends, with a confirmation vote expected on Wednesday evening. “Senator Warren was giving a lengthy speech,” McConnell said. “She had appeared to violate the rule. She was warned. She was given an explanation. Nevertheless, she persisted.”

The effort to silence Warren largely backfired, turning the Massachusetts senator, briefly, into a social-media sensation. After being silenced on the Senate floor, Warren stepped outside to read the full 10-page letter in a Facebook Live video that has been viewed more than 5 million times as of Wednesday morning.

Supporters also flocked to Twitter to share the King letter in its entirety, as well as to rebuke Senate Republicans, using the hashtag #LetLizSpeak.