The day after the second presidential debate, Democratic nominee Hillary Clinton speaks to and meets voters at Wayne State University in Detroit. (Melina Mara/The Washington Post)

A buoyant Hillary Clinton promised Monday to give Americans “something to vote for, not just something to vote against,” but made clear that Democrats see new opportunity to press the case against Republican Donald Trump in the final four weeks of the election contest.

Riding high as Republicans sank into a historic internal crisis over Trump’s behavior, Clinton strode into the nation’s Rust Belt, pledging to push a “renaissance” of advanced manufacturing and sharply criticizing Trump’s commitment to blue-collar workers.

In her first campaign event since Sunday’s second debate, Clinton acknowledged the ugliness of the face-off with Trump, telling an enthusiastic crowd of 3,500 here: “Bet you haven’t seen anything like that before.”

Campaigning in Michigan, where Trump’s once-promising position had already become a long shot before the revelation of lewd comments the Republican nominee had made about women, Clinton urged voters not to let disgust at ugly politics turn them off from participating.

“That’s what the other side wants you to feel, that ‘I’m not going to vote because it’s so nasty,’ ” she told her audience at Wayne State University. “ That’s the main reason to vote, to make it clear that we’re not going to put up with that kind of attitude.”

She did not mention the divide among Republicans, best encapsulated in House Speaker Paul D. Ryan’s announcement Monday that he would no longer campaign with or defend his party’s presidential nominee. That was read as an offer of amnesty for other elected Republicans who decide to renounce Trump or keep their distance.

Several dozen national or state-level Republicans have denounced Trump or rescinded support since the comments, in which Trump described forcing himself on women sexually, were first reported by The Washington Post on Friday.

“Donald Trump spent his time attacking when he should have been apologizing,” Clinton said of a debate in which Trump brought up allegations of sexual conduct by President Bill Clinton, called Hillary Clinton the “devil” and suggested he’d jail her if elected president.

Trump signaled Monday that he will continue with the combative posture he showed at Sunday’s debate. He attacked Ryan on Twitter, writing that speaker from Wisconsin should “spend more time on balancing the budget, jobs and illegal immigration and not waste his time on fighting Republican nominee.” Ryan told House Republicans on Monday that he will not campaign with Trump or defend him.

At an afternoon rally in Ambridge, Pa., Trump continued to attack Clinton over her husband’s marital indiscretions, citing allegations of sexual improprieties against the former president while dismissing intense criticism over his own treatment of women.

“As I outlined last night, Bill Clinton was the worst abuser of women ever to sit in the Oval Office. He was a sexual predator,” Trump said. “For decades Hillary Clinton has been familiar with her husband’s predatory behavior and, instead of trying to stop him, she made it possible for him to take advantage of even more women.”

Clinton moved ahead by double digits Monday in the first large national poll since The Washington Post reported Friday on a 2005 recording of Trump using extremely crude language to describe women and boasting that he could get away with uninvited physical advances because he was a celebrity.

The NBC-Wall Street Journal poll shows Clinton with a 14-point lead over Trump in a two-way race and 11 points ahead in a four-way contest with third-party candidates who cannot compete in every state.

The RealClearPolitics average of recent polls shows a more modest six-point gap, but that is still a larger margin than many Clinton strategists and allies had predicted with fewer than 30 days to go before Election Day and many states allowing early voting.

“There’s a lot of work to be done,” Clinton said. “This is a time to come together in these last 29 days. We’ve got to make good things come together in America, and I believe that with all my heart.”

Clinton urged Michigan voters to register before the deadline Tuesday. She later addressed an estimated 18,500 people at what appeared to be the largest rally of her campaign, at Ohio State University in Columbus. The race has been a dead heat in Ohio, where Trump has lost a lead that looked comfortable at roughly five points just two weeks ago. The RealClearPolitics average now has Clinton ahead by half a percentage point.

For reference, Ohio is considered the second-hardest battleground state for Clinton to win, after Iowa, where Trump still leads.

A Clinton campaign official said Trump’s sinking fortunes are unlikely to change any fundamental element of Clinton’s strategy, which relies on success in seven battleground states atop states where she is confident of winning.

But with Trump bleeding support from high-profile Republicans, Clinton’s campaign launched a series of television ads Monday seeking to persuade rank-and-file GOP voters to side with the Democratic nominee in November.

The four ads, airing in battlegrounds states, seek to highlight different concerns about Trump, with testimonials from Republican voters as to why they believe he is unqualified to be president.

The new ads feature a former Reagan administration official, a Republican mother of a child with autism, a Republican Army veteran and a former local Republican Party official.

Although the push to appeal to Republicans began months ago, Clinton aides see a larger opening in the wake of Trump’s uneven performance in the first presidential debate and the widespread condemnation of his recorded comments.

Aides said the new 30-second ads are airing as part of a national cable campaign and as part of existing ad campaigns in Florida, Iowa, Nevada, North Carolina, Ohio and Pennsylvania.

Clinton’s campaign sees a chance to shore up support among white working-class men — Trump’s strongest constituency. And that includes Republicans.

“We are getting more and more support, not just from Democrats but from independents and Republicans,” Clinton claimed here.

Before leaving Wayne State University, the event site, Clinton met briefly with Dan Gilbert, owner of the Cleveland Cavaliers and a Republican, according to an aide, who provided no additional details.

Before last week, she faced long odds with working-class white voters in the industrial Midwest and elsewhere. Polls have showed white voters without college degrees breaking heavily toward Trump — and harboring deep-seated animosity toward Clinton, the former first lady, senator from New York and secretary of state.

As Bill Clinton did during a bus tour of working-class Ohio last week, Hillary Clinton focused on an issue that her campaign thinks could undermine Trump’s appeal to working-class voters here and in other states that have shed manufacturing jobs: reports that the real-estate developer used dumped Chinese steel for construction projects rather than acquiring it from companies in the struggling U.S. Rust Belt.

“China has been dumping cheap steel into our markets for too long,” Clinton said. “When people like Donald Trump buy it, it kills good jobs. . . . How does Trump look these workers in the eye? How does he brag about big, tall buildings when he’s putting American workers out of work.”

During the course of the half-hour rally, Clinton also pledged to foster the creation of advanced manufacturing jobs, including in “clean energy,” and to address “kitchen-table issues that keep families up at night.” She also reminded the crowd of her support of President Obama’s bailout of the auto industry.

“We know who Donald Trump is, but the real question for us is, who are we?” Clinton said. “I would argue we are not who he is.”

Gearan reported from Washington. Sean Sullivan in Washington and Jose A. Del Real in Ambridge, Pa., contributed to this report.