The rule is as old as the printing press. If you want to make someone read something, tell them they can't. From the Associated Press:

Immediately after being shut down, Warren took to Facebook Live to read the Coretta Scott King letter. As of this post, the video had 7 million viewers.

Within the last hour, in a floor address, Senate Minority Leader Chuck Schumer, D-N.Y., accused Republicans of overzealousness.

“Senator Warren wasn’t hurling wild accusations, she was reading a thoughtful and considerate letter by a leading civil rights leader,” Schumer said.

The Democratic leader said Rule 19 was being enforced selectively – and pointed to Sen. David Perdue, R-Ga., (though not by name) as an example.

After Schumer had become emotional during a statement of protest against President Donald Trump’s travel ban, Perdue had said -- on the chamber floor -- that the New York senator’s tears “belonged at the Screen Actors Guild Awards.”

“But I didn’t run to the floor to invoke Rule 19,” Schumer said.

Republican leaders held their ground on Wednesday morning.

Senate Majority Whip John Cornyn, R-Texas, said a "line was crossed last night" by Warren when she quoted King and the late Sen. Ted Kennedy.

"A senator can't evade that rule by somehow claiming, 'well, these weren't my words. I was reading what somebody else said,'" he said in a speech on the Senate floor.

"I hope that maybe we've all been chastened a little bit and maybe we've all learned a little bit of a lesson here," he said. "I would yearn for the day when the Senate and frankly the country as a whole would pull back from the abyss of recrimination, personal attacks and we would get back to doing what this institution was designed to do, which is to be a great body for deliberation and debate."

Reading of Coretta Scott King’s letter even spread this morning to the state Capitol, where state Sen. Vincent Fort squeezed as much as he could into the five minutes (and slightly more) allotted to him:

"You can't shut down an idea. You stop one debate, you create one million debates. As a matter of fact, maybe we should thank Mr. McConnell for his obstruction. Because what he did is make Coretta Scott King's letter more popular, even more widespread."

Fort’s actions were rebutted on the floor minutes later by state Sen. Josh McKoon, R-Columbus, who said Warren broke U.S. Senate rules and was properly punished.

“She was disparaging a senator from the well,” said McKoon, who called her remarks an “unbelievable character assassination.”

“We’re seeing historic procedures taken…to do anything possible to obstruct the duly elected President of the United States,” McKoon said. “It was entirely appropriate for the U.S. senate to take that action.”