Hours before Sen. Elizabeth Warren (D-Mass.) read a letter on the Senate floor Tuesday night that would make her Wednesday’s buzziest political story, her publisher sent a tweet.

Warren’s new book, “This Fight Is Our Fight,” will be out in April. The Boston Globe, which first reported the book’s release date, said “the book’s promoters say it will trace the development of the middle class from the New Deal to the Trump administration. Warren will outline her ideas for how the government can better serve the middle class and weave in stories from her time in the Senate and the experiences of Americans who have struggled under the current economic policies.”

Warren shared the news on her Facebook page less than an hour later.

By Wednesday afternoon, Warren’s forthcoming book was No. 1 in the Amazon bestseller list in the U.S. Congresses category. Her kindle edition was No. 2. The Globe reported some of the book’s proceeds will be donated to food banks in Massachusetts.

Being on the bestsellers list is not that unusual for Warren. Her 2014 book, “A Fighting Chance,” was also a New York Times bestseller, and on Wednesday, versions of it appear on the top 10 Amazon’s congressional category bestseller list four times.

The book’s release is newsworthy in itself, given Warren’s every move is consistently watched by political analysts through the lens of whether she’ll run for president in 2020.

Back in the Senate, what happened next to Warren also attracted attention. A lot of it.

Warren went to the Senate floor a little before 7 p.m. to officially announce her opposition to Sen. Jeff Sessions (R-Ala.), President Trump’s pick to be attorney general. Senate Democrats, unable to block Sessions’s confirmation, have been delaying the inevitable by demanding several days of debate per nominee. Throughout the day Tuesday, several other Senate Democrats had also announced their opposition to Sessions.

When it was Warren’s turn, she bolstered her arguments with a letter from the late senator Edward M. Kennedy (D-Mass.), who voted against Sessions for a judgeship in 1986. (Sessions, then a U.S. attorney, did not get the judgeship after colleagues of his accused him of saying racially insensitive things.) Kennedy declared Sessions “a disgrace to the Justice Department and he should withdraw his nomination and resign his position,” a line Warren read out loud.

At that moment, the presiding Senate officer, Sen. Steve Daines (R-Mont.), warned Warren she was in danger of violating Rule 19, a century-old rule born out of a fist fight that prohibits senators from attacking the character of another senator. Since its inception, it’s been used very sparingly.

In an interview Wednesday with CNN, Warren said she was surprised by Daines’s warning. “I thought: ‘I don’t see it, but alright.’ Then I turn to read Coretta Scott King’s letter.”

In that letter, King, the widow of Martin Luther King Jr., also urged the Senate Judiciary Committee to oppose Sessions’s nomination for a federal judgeship, in equally fiery language as Kennedy: “Mr. Sessions has used the awesome power of his office to chill the free exercise of the vote by black citizens,” she wrote, referencing a voting rights case Sessions prosecuted as U.S. attorney.

That line in King’s letter was the tipping point for both Senate Republicans and Warren’s turn in the spotlight. Senate Majority Leader Mitch McConnell (R-Ky.) walked onto the Senate floor minutes later, asked Warren to stop speaking, called all senators to the floor and took a vote (strictly along party lines) to deny her ability to speak on the floor for the rest of the debate on Sessions, pursuant to Rule 19.

The clash quickly became a national story. Warren read the King letter on Facebook Live in an adjacent room. She spoke to CNN late that night. #LetLizSpeak trended on Twitter. Her campaign sent out a copy of the letter to its supporters with its version of what happened. Other Democratic groups sent out fundraising emails. Senate Minority Leader Chuck Schumer (D-N.Y.) defended Warren on the Senate floor.

CNN’s Manu Raju asked Warren on Wednesday how she felt about all the buzz on the left surrounding her rare rebuke. “Some of the Democrats are also trying to raise money off of this. Are you OK with that, doing this? And how much money has — have you raised for your campaign out of this?”

Warren’s response: “I have — I have no idea. This is about trying to get people to read Coretta Scott King’s letter.”