John C. Danforth, a former Republican senator from Missouri, had once viewed Sen. Josh Hawley (R-Mo.) as a “once-in-a-generation” talent — a young, upstart politician with a promising future in Washington.

Yet after a mob of Trump supporters burst into the Capitol on Wednesday, Danforth said that campaigning for Hawley to take his old seat was “the worst mistake I ever made in my life.”

Hawley had been the first senator to announce he would object to President-elect Joe Biden’s victory, citing baseless claims of mass election fraud. So when the rioters bashed inside, attempting to overturn the election, it was clear who was at fault, Danforth said.

“But for him it wouldn’t have happened,” Danforth told the Kansas City Star. He made the certification vote “a way to express the view that the election was stolen. He was responsible.”

The former senator was far from the only one to lay blame on his former protege. In the span of about five hours on Thursday afternoon, Hawley was denounced by one of his top donors, dropped from a book deal and lambasted by several Missouri Republicans. Calls for him to resign poured in from the editorial boards of Missouri’s two major newspapers and students at the law school where he once taught.

His office did not immediately respond to a request for comment from The Washington Post late on Thursday. But in a statement to KSDK, the 41-year-old senator was unrepentant about his role in challenging Biden’s electoral college victory.

“I will never apologize for giving voice to the millions of Missourians and Americans who have concerns about the integrity of our elections,” he said. “That’s my job, and I will keep doing it.”

Capitol Police were unable to stop a breach of the Capitol. Washington Post reporter Carol Leonnig and a former Senate Sergeant at Arms describe the events. (The Washington Post)

In leading the Senate’s objection to Biden’s electors alongside Sen. Ted Cruz (R-Tex.), Hawley has rapidly lifted his national profile, amassing the kind of attention that many observers speculate could pave the way to a future White House bid. But it has also arguably brought him more blame for the riots than anyone besides President Trump.

As The Washington Post’s Kim Bellware reported, Hawley raised his fist in solidarity when he strode past Trump supporters outside the Capitol on Wednesday afternoon. Hours later, part of that crowd invaded the building, bringing the certification process to a sudden halt. But when Congress reconvened later in the day, Hawley continued with his objections.

After witnessing the “disturbing, deadly insurrection,” Simon & Schuster on Thursday said it had canceled a book deal with the senator, who had been first elected to Congress in 2018.

“We take seriously our larger public responsibility as citizens, and cannot support Senator Hawley after his role in what became a dangerous threat to our democracy and freedom,” a statement from the publishing house said.

The senator had been set to release a book with Simon & Schuster titled “The Tyranny of Big Tech,” about how big tech companies “represent the gravest threat to American liberty since the monopolies of the Gilded Age,” The Post’s Amy B Wang reported.

Hawley responded by decrying the publisher as a “woke mob” and pledging to fight its “cancel culture” in court.

“This could not be more Orwellian,” he said in a statement on Twitter. “This is the Left looking to cancel everyone they don’t approve of.”

Yet much of the backlash against Hawley was in fact coming from other Republicans — and in at least one case, from the man whose donations fueled the senator’s political ascent.

David Humphreys, a businessman and onetime conservative Missouri megadonor, said Thursday that Hawley should be censured for his use of “irresponsible, inflammatory and dangerous tactics.”

“He has now revealed himself as a political opportunist willing to subvert the Constitution and the ideals of the nation he swore to uphold,” Humphreys, president and chief executive of Tamko Building Products, said in a statement to the Missouri Independent.

According to the Independent, Humphreys’s donations amounted to about one-third of Hawley’s total fundraising for his successful 2016 campaign for Missouri attorney general. Two years later, the megadonor’s family contributed an estimated $2 million to groups supporting Hawley’s Senate bid.

On Twitter, state Rep. Shamed Dogan, a Republican, wrote that he regretted voting for Hawley.

“His refusal to accept the legitimacy of Joe Biden’s election, even after today’s violence, is an embarrassment,” Dogan said.

Not unsurprisingly, the strongest rebukes on the social media platform came from Democratic lawmakers in Congress, including Reps. Cori Bush (Mo.), Joaquin Castro (Tex.) and Alexandria Ocasio-Cortez (N.Y.). All three called for Hawley to resign.

The Kansas City Star’s editorial board, which had once endorsed Hawley as the “clear choice” in the 2018 Republican Senate primary, took a more pragmatic view.

“If Missouri Sen. Josh Hawley had a conscience, he’d resign,” the editorial’s headline said. Instead, “he’ll have to be removed.”

Bellware and Wang contributed to this report.