Donald Trump issued a breathtaking call to arms Thursday as he emphatically denied allegations that he groped and kissed multiple women without their consent, charging that his accusers were part of a global conspiracy to extinguish his outsider movement.

Scrambling to turn around his floundering campaign, Trump declared war on the news media and multinational corporations, ­alleging that they are colluding with Democratic nominee ­Hillary Clinton to orchestrate “the single greatest pile-on in history” and undermine his ­campaign, which he said was an “existential threat” to the global establishment.

“The Clinton machine is at the center of this power structure,” the Republican nominee said at a rally in West Palm Beach, Fla. “Anyone who challenges their control is deemed a sexist, a racist, a xenophobe and morally deformed. They will attack you, they will slander you, they will seek to destroy your career and your family. . . . They will lie, lie, lie.”

Trump’s fiery invective came just minutes after first lady Michelle Obama tried to summon the morality of a nation by saying that Trump’s degrading comments about women were an affront to all citizens.

The dueling speeches made for a remarkable moment in a roiling presidential campaign and signaled that the final 25 days would focus not on policy or ideology but on character.

Donald Trump insists he's never acted the way he described in the lewd comments he made on tape in 2005, but since the Oct. 9 debate, multiple women have accused him of forcing himself on them sexually. Trump's TV surrogates are doing their best to defend him. (Peter Stevenson/The Washington Post)

The first lady, exasperated and angry, said video of Trump in 2005 bragging about leveraging his stardom to force himself upon women “has shaken me to my core.” Although careful never to mention Trump by name, Obama sternly admonished him for behavior she called “cruel,” “sick” and devoid of basic human decency.

“This is not politics as usual,” Obama said at a rally for Clinton in Manchester, N.H. “This is disgraceful, it is intolerable, and it doesn’t matter what party you belong to — Democrat, Republican, independent — no woman deserves to be treated this way. None of us deserves this kind of abuse.”

President Obama picked up where his wife left off, denouncing Trump and casting this election as “about affirming democracy.”

Obama also sought to shame Republicans who stood by silently during Trump’s ascent. “You claim the mantle of the party of family values, and this is the guy you nominate? And stand by? And endorse? And campaign with?” he said at an Ohio Democratic Party dinner in Columbus.

In his Florida speech, Trump framed his candidacy in epic, global terms. He said the Nov. 8 election represents “a crossroads in the history of our civilization,” with his populist movement fighting to upend “radical globalization and the disenfranchisement of working people.”

Trump hopes his revolutionary message will galvanize his base of aggrieved working-class whites to vote in historic numbers and help him overcome what polls suggest could be an insurmountable deficit to Clinton with virtually every other demographic group.

Republican presidential nominee Donald Trump responded to a former People magazine writer who wrote that he kissed her without her consent in 2005 saying, "I don't think so." (The Washington Post)

Trump’s remarks, which he read from a teleprompter, were laced with the kind of global conspiracies and invective common in the writings of the alternative-right, white-nationalist activists who see him as their champion. Some critics also heard echoes of historical anti-Semitic slurs in Trump’s allegations that Clinton “meets in secret with international banks to plot the destruction of U.S. sovereignty” and that media and financial elites were part of a soulless cabal out to destroy “our great civilization.”

“It’s a global power structure that is responsible for the economic decisions that have robbed our working class, stripped our country of its wealth and put that money into the pockets of a handful of large corporations and political entities,” Trump said.

The speech bore the imprint of Stephen K. Bannon, the Trump campaign’s chief executive, who until recently was the executive chairman of Breitbart, a conservative website that serves as the virtual town square of the alt-right movement.

Jonathan Greenblatt, chief executive of the Anti-Defamation League, tweeted that Trump “should avoid rhetoric and tropes that historically have been used against Jews” and “keep hate out of campaign.”

Trump leveled searing charges against Clinton and her husband, former president Bill Clinton. He accused them of engaging in “a massive coverup of widespread criminal activity at the State Department and the Clinton Foundation.”

“The Clintons are criminals,” Trump said. “Remember that. They’re criminals.”

Trump dismissed the claims of sexual harassment made by several women Wednesday as an “absolute horror show of lies” and labeled his accusers — as well as the journalists who reported their stories — “horrible, horrible liars.” He claimed he could prove that their accusations were false, but he declined to detail his evidence.

Trump also claimed that the women were “put forward” by “the Clinton machine,” although there is no evidence that the Clinton campaign was behind the women going public with their accusations. Two women who told the New York Times that Trump touched them inappropriately said they came forward after watching Trump, in Sunday night’s debate, deny ever taking such actions.

In his Florida speech, Trump lashed out at former People magazine reporter Natasha Stoynoff, who wrote in a first-person account published Wednesday that Trump kissed her without her consent at his Mar-a-Lago resort in Florida in 2005 when they were alone before an interview with him and his then-pregnant wife, Melania.

“Take a look, you take a look,” Trump urged his supporters. “Look at her. Look at her words. You tell me what you think. I don’t think so.”

Clinton, who was in California on Thursday raising money, told donors at a San Francisco event that the accounts about Trump were “disturbing.”

“The whole world has heard Trump brag about how he mistreats women, and the disturbing stories just keep coming,” Clinton said. “But it’s more than just the way he degrades women, as horrible as that is. He has attacked immigrants, African Americans, Latinos, people with disabilities, POWs, Muslims and our military, which he’s called a disaster. There’s hardly any part of America that he’s not targeted.”

The abuse allegations have put Trump further on the defensive at a time when he trails Clinton badly in key battleground states and has been abandoned by dozens of elected Republican officials. House Speaker Paul D. Ryan (R-Wis.) said Monday he would no longer defend Trump or campaign with him, though he has not withdrawn his endorsement.

Democrats on Thursday marveled at what they see as Clinton’s good fortune: The allegations against Trump, and his decision to dig in and rebut them one by one, distract from damaging revelations that have emerged from the WikiLeaks hack of Clinton campaign emails.

Paul Begala, a Democratic strategist and adviser to the pro-Clinton super PAC Priorities USA, said Trump was self-destructing.

“To quote the late great Nelson Mandela, it’s like drinking poison and thinking it’s going to hurt your enemy,” Begala said. “He’s a billionaire tycoon in a total meltdown, and he’s going to try to take as many people down with him. It’s not a political strategy, but it will be an unlovely 26 days until we dispatch him to the ash heap of history.”

Trump also faced new criticism over vulgar comments he made about forcing himself physically on women in a 2005 video, first reported by The Washington Post last Friday. In the video, Trump is heard talking about soap-opera actress Arianne Zucker on a hot microphone right before meeting her, and she told NBC News that Trump’s words were “offensive comments for women, period.”

Trump was asked at a presidential debate Sunday whether he ever did the things he talked about on the tape, including grabbing women “by the p---y.” He said, “No, I have not.”

But Trump’s answer is at odds with the accounts of the four women who spoke in the Wednesday reports. 

Early Thursday, Trump’s campaign released a letter from lawyer Marc E. Kasowitz demanding a retraction by the Times and threatening a lawsuit. In response, Times general counsel David E. McCraw sent Kasowitz a letter Thursday defending the newspaper’s reporting. If Trump disagrees with it, McCraw wrote, “we welcome the opportunity to have a court set him straight.”

Michelle Obama referenced the allegations against Trump and his 2005 conversation with “Access Hollywood” host Billy Bush in her Manchester speech, which was perhaps her most personal and indignant of the campaign season.

“It’s not something we can just sweep under the rug as just another disturbing footnote in a sad election season,” Obama said. “Because this was not just a ‘lewd conversation.’ This wasn’t just ‘locker-room banter.’ This was a powerful individual speaking freely and openly about sexually predatory behavior.”

Obama said this campaign is teaching important lessons to the nation’s children.

“If we let Hillary’s opponent win this election, then we are sending a clear message to our kids that everything they’re seeing and hearing is perfectly okay,” she said. “We are validating it. We are endorsing it. We’re telling our sons that it’s okay to humiliate women. We’re telling our daughters that this is how they deserve to be treated.”

Jose A. DelReal in West Palm Beach contributed to this report.