On Wednesday morning, two Democratic senators did something that had been declared out of bounds by their Republican colleagues just the night before — they read a letter from Coretta Scott King on the Senate floor.

Written in 1986, the letter criticizes the civil rights record of Sen. Jeff Sessions (R-AL), President Trump’s nominee for attorney general. When Sen. Elizabeth Warren (D-MA) read from it late Tuesday night, Senate Majority Leader Mitch McConnell (R-KY) found her in violation of Senate Rule 19 — an obscure and rarely enforced restriction barring senators from using “any form of words [to] impute” the motives of another senator during floor debate. The Republican Senate then voted to prevent Warren from speaking for the rest of the debate over Sessions’s confirmation.

But around 10 the next morning, Sens. Tom Udall (D-NM) and Sherrod Brown (D-OH) went to the floor and read King’s letter, including portions of it that directly attacked Sessions. This time, McConnell decided against using Rule 19 to cut off Udall or Brown — even though both of the Democratic senators were certainly also “imputing” Sessions’s record.

What changed since Warren’s speech was about 12 hours of relentlessly negative press and social media coverage about the decision to censure her. “It backfired badly," said Sarah Binder, a congressional scholar at the Brookings Institution. "McConnell has every incentive to get these nominees into office as quickly and quietly as possible. By trying to do it more quietly, he in fact ginned up much more attention."

Mitch McConnell flies the white flag after censure backfires

When Warren spoke on the floor of the Senate Tuesday night, only a few hundred people were tuned in to C-SPAN. There was almost nobody in the Senate chamber watching what was a non-event, as each member of the Senate Democratic caucus delivered his or her stump speech opposing Sessions. Warren herself appeared caught off guard as McConnell and Sen. Steve Daines (R-MT) told her she would not be allowed to speak for the rest of the debate over Sessions’s nomination.

The ensuing backlash against McConnell’s decision turned a routine and otherwise unremarkable floor speech into a national media controversy.

After she was cut off, Warren recorded a Facebook Live video on the steps of the Capitol decrying McConnell’s decision; it got more than 3 million views. Democratic senators beat the drum of outrage, rallying to Warren’s defense:

This is unreal. Senate Republicans have ruled that any Democrat that criticizes Sessions' record will be stripped of the right to speak. https://t.co/At5fqUkVWF — Chris Murphy (@ChrisMurphyCT) February 8, 2017

At 11 pm Tuesday, Warren’s speech was the lead story on CNN and then again on CNN.com throughout Wednesday. It got widespread coverage across the political media landscape, and even received reasonably sympathetic coverage from the right-leaning Fox News. #StandWithLiz trended on Twitter.

Warren’s Facebook page gained nearly 3 million followers essentially overnight. Encouraged by celebrities, activists on social media reported calling McConnell’s office and reading King’s letter out loud. The Democratic National Committee chair used the incident to raise money:

When Sen. Brown tried to read from King’s letter Wednesday morning, he wasn’t sure if McConnell would retaliate against him the way he had against Warren, according to a Brown spokesperson. But McConnell decided to let the speeches proceed uninterrupted, suggesting that he realized the censure was helping Democrats organize and mobilize their base — at least more than letting Warren speak would have, Democrats on the Hill say.

“It’s clear this backfired, and now they’re trying to kill the story,” said one Senate Democratic aide.

Democrats have little to gain, and everything to lose, from supporting Trump

McConnell’s backpedaling won’t change much about Sessions’s confirmation — he has enough votes to get through on a party-line vote this week. But the decision does underscore the steadfast opposition Senate Democrats have shown against Trump, propelled in large part by persistent progressive outrage at the Trump administration’s actions.

“There’s a bit of win-win going on for the Democrats: Be responsive to a base that’s very mad, pull out the stops by showing you’re fighting, and get people mad and revved up for future legislative battles,” says Binder.

This dynamic has changed dramatically since the confirmation hearings began.

In mid-January, Sen. Cory Booker (D-NJ) became the first senator in US history to testify against the Cabinet confirmation of another senator when he did so against Sessions at a judiciary committee hearing. The historic breach of Senate norms was met with shock on Capitol Hill: The Washington Post ran an in-depth one-on-one interview in which Booker explained how he agonized over the choice before deciding it was the right thing to do. His speech against Sessions was carried live on the major primetime television networks. Dozens of protesters filled the halls outside Booker’s speech in the Dirksen Senate Office Building.

But less than two weeks later, Booker was under fire again — not from the right for refusing to cooperate with Trump, but from the left for voting for some of Trump’s nominees. Similar criticism erupted against Sens. Brown and Warren when they decided to vote to confirm Ben Carson to run the Housing and Urban Development Department.

Booker’s attack on Sessions was an early sign of what was to come — now every single Democratic senator except Sen. Joe Manchin (D-WV) plans to vote against him, according to the Washington Post. Far more Senate Democrats plan to vote against the remaining Trump nominees than voted for the initial nominees who were cleared.

In part, that’s because Trump’s more controversial nominees have taken longer to move through the confirmation process than the ones Democrats had fewer objections to. But it also reflects how mass grassroots resistance in the first three weeks of Trump’s administration has given Senate Democrats every incentive to do what they can to attack the president’s nominees, regardless of Senate norms and customs.

“They know these [Trump] nominees are all going to get confirmed, so these are opportunities for them to send a message to their base that they’re hearing their demand to stand up,” Binder says. “And there’s very little cost except some negative tweets from the president, who their voters don’t like anyway.”