McConnell used Senate Rule XIX to lodge an objection to Warren's remarks, as the Senate then voted to prevent Warren from speaking for the rest of the day.
Warren had also read a statement given back in 1986 by Sen. Edward Kennedy (D-MA), which called Sessions a "disgrace."
After listening to weeks of criticism of Sessions, the Warren speech was the straw that broke the camel's back for some in the GOP.
"We're treating him like he's some kind of terrible person," complained Sen. Orrin Hatch (R-UT). "We should be ashamed of ourselves."
"I'm the one that entered the objection," said Sen. James Risch (R-ID).
"We have rules around here, and the rules are very clear that you don't impugn another Senator," said Risch, in a clearly aggravated tone.
While Republicans vented their frustration over the treatment of Sessions, Democrats used the Warren rebuke as an immediate rallying cry.
"The suggestion that reciting the words of the great Coretta Scott King would invoke Rule XIX and force Sen. Warren to sit down and be silent is outrageous," said Sen. Kamala Harris (D-CA), as others joined in.
"She wasn't just quoting something that she heard on the street," said Sen. Corey Booker (D-NJ). "She was quoting Coretta Scott King."
Several hours later, Sen. Jeff Merkley (D-OR) read much of the King letter again on the floor, including a final paragraph that argued against confirmation for Sessions; no GOP Senator rose to challenge his action.
The letter from Mrs. King had been sent in 1986 to the Chairman of the Senate Judiciary Committee, Sen. Strom Thurmond (R-SC). Democrats pointed out that basically meant the letter was a Senate document.
If Republicans had just ignored Warren's speech, very few people would have probably heard about the Coretta Scott King letter from March of 1986.
The Senate will vote Wednesday evening on the Sessions nomination.