ST. LOUIS — Early on in Sunday’s debate, a fly drifted into the frame and came to rest, just for a moment, at the base of Hillary Clinton’s left eyebrow.

She blinked, flicked her head, and kept talking.

This was the Democratic nominee's posture for more than an hour and a half here at Washington University as Donald Trump put on one of the more hostile performances of this year's divisive presidential race. He called his opponent the "devil," said she had "tremendous hate in her heart." He vowed to put her in prison, raised her husband's infidelities, and brought women who alleged Bill Clinton sexually abused them into the debate hall. He paced the stage as she spoke. He lied about his opposition to the war in Iraq and asserted that had he been president, the late Captain Humayun Khan would still be alive.

When the debate was halfway through, one of Clinton's aides back in Brooklyn snapped. "hey, @realDonaldTrump — regarding your claim that Captain Khan would be alive if you were president," tweeted spokesperson Jesse Lehrich.

"go fuck yourself."

The harsh tweet, which Lehrich later apologized for, amounted to what Clinton managed to largely avoid in the second presidential debate, a town hall–style forum that finally brought forth some of the personal attacks Trump has vowed to make for weeks.

The debate followed a tumultuous weekend of shifting political ground. After old footage emerged of Trump saying, for instance, that he could “grab” women “by the pussy,” Republican officials abandoned their party’s nominee in large numbers. And on Sunday, Trump stunned most people in politics, appearing with women who had alleged that Clinton’s husband had sexually abused them.

“If you look at Bill Clinton — far worse. Mine are words, and his was action. His was what he's done to women. There's never been anybody in the history politics in this nation that's been so abusive to women,” Trump said, answering a question about the bombshell 11-year-old raw footage surfaced Friday by the Washington Post.

“Bill Clinton was abusive to women.”

Trump went on to accuse his opponent of “viciously” taking down those women. Three of them — Paula Jones, Kathleen Willey, and Juanita Broaddrick, who alleges that Bill Clinton raped her in the late 1970s — were seated inside the debate hall at the Republican nominee's invitation.

As Trump invoked their stories — “I think she should be ashamed of herself, if you want to know the truth” — Clinton held a muted gaze on her opponent.

After the first debate, Trump and his supporters boasted that he had restrained himself in not attacking Clinton over Monica Lewinsky, which turned into days of coverage about whether this time, Trump really would revisit the topic. Ahead of the second match-up, Clinton and a team of senior advisers prepared for an uglier and more personal debate.

The response she offered Sunday did not touch on the substance of Trump's claims. "He gets to run his campaign any way he chooses," she began. "He gets to decide what he wants to talk about — instead of answering people's questions."

Bill Clinton's extramarital activity and personal history has made for tense moments on the trail for some 17 months now, partly as a reflection of the changing politics of sexual harassment and assault allegations. But Trump put the former president at the center of his presidential campaign early in the race, and on occasion, protesters and voters in the crowd have confronted the former first lady in unexpected turns at events with questions (or jeers) about the claims made by Jones, Broaddrick, and Willey.

Often, Clinton is the least uncomfortable person in the room, appearing unfazed as she delivers a straightforward answer, moving on as if the moment never happened. Longtime aides refer often to Clinton’s ability to “compartmentalize” in real time.

After the debate, Clinton’s aides dismissed the women’s presence as a campaign tactic meant to upend their candidate’s performance.

“The stunt didn’t work,” said campaign manager Robby Mook, speaking to reporters aboard Clinton’s “Stronger Together” campaign plane on the way back east.

“Hillary just plowed forward.”