SENATE Republicans have silenced Democratic senator Elizabeth Warren for criticising attorney general nominee Jeff Sessions with the words of Coretta Scott King from three decades ago.

The Massachusetts politician, whose name has been prominent in speculation about the 2020 presidential race, was given a rare senate rebuke for impugning a fellow senator late on Tuesday and barred from saying anything more on the senate floor about the nominee.

The chamber is debating the Alabama Republican’s nomination for attorney general, with Democrats dropping senatorial niceties to oppose Mr Sessions and Republicans sticking up for him.

Warren produced a three-decade-old letter in which the civil rights leader wrote that Mr Sessions as an acting federal prosecutor in Alabama used his power to “chill the free exercise of the vote by black citizens”.

Quoting King technically put Warren in violation of senate rules for “impugning the motives” of Mr Sessions, though senators have said far worse. And Warren was reading from a letter that was written 10 years before Sessions was even elected to the senate.But top senate Republican Mitch McConnell invoked the rules.

After a few parliamentary moves, the Republican-controlled senate voted to back him up. Now Warren is forbidden from speaking again on Sessions’s nomination.

Democrats seized on the incident to claim that Republicans were muzzling Warren, sparking liberals to take to Twitter to post the King letter in its entirety.

Warren argued: “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.”

Warren was originally warned after reading from a statement by former senator Edward Kennedy that labelled Sessions a disgrace. Democrats pointed out that McConnell did not object when Republican senator Ted Cruz called him a liar in a 2015 dustup.