St. Louis (AFP) - In a bombshell development just hours before Donald Trump debates Hillary Clinton to try to salvage his presidential candidacy, the Republican nominee staged a surprise appearance with women who have accused Bill Clinton of sexual misconduct.

Trump is facing a make-or-break moment after his own lewd boasts about sexually assaulting women, caught on tape in 2005 and made public Friday, brought sweeping condemnation from within his own party and calls for him to step aside just a month before Election Day.

With tens of millions of Americans expected to watch the televised showdown, Trump may have been expected to show contrition as he seeks to move beyond the crisis.

But his last-minute event was seen as an intense and defiant provocation -- and a strong suggestion he would bring up the sexual behavior and misconduct accusations against his White House rival's husband.

Introduced by Trump as "very courageous women," his invited speakers included Paula Jones, a former government employee in Arkansas who sued Bill Clinton for sexual harassment, and Juanita Broaddrick, also of Arkansas, who claims that Clinton raped her in 1978.

"Mr. Trump may have said some bad words," Broaddrick said, seated next to Trump at a panel staged for a handful of media, and broadcast live on Facebook.

"But Bill Clinton raped me, and Hillary Clinton threatened me. I don't think there's any comparison."

It was the latest shock twist in an unprecedented weekend of political crisis that saw Republican lawmakers and governors abandon their own party's presidential nominee in droves.

Trump sought to stem the bleeding with a formal apology -- the first of his insult-driven campaign -- over the 2005 hot mic that caught him making vulgar remarks about being able to "do anything," including groping womens' crotches, because he is famous.

Even as criticism swelled and surrogates struggled to contain the damage, Trump threw caution to the wind.

"So many self-righteous hypocrites. Watch their poll numbers -- and elections -- go down!" Trump said on Twitter.

Clinton's camp dismissed Trump's decision to trot out Bill Clinton's accusers as an "act of desperation."

"We're not surprised to see Donald Trump continue his destructive race to the bottom," her communications director Jennifer Palmieri said in a statement.

Hillary is "prepared to handle whatever Donald Trump throws her way."

- 'Insecure' -

During a campaign event in Illinois earlier Sunday, President Barack Obama weighed in saying the man vying to succeed him was "insecure."

"Demeaning, degrading women, but also minorities, immigrants, people of other faiths, mocking the disabled... That tells you a couple things," Obama said.

"It tells you that he is insecure enough that he pumps himself up by putting other people down. Not a character trait that I would advise for somebody in the Oval Office."

Mike Pence, Trump's running mate, suspended his campaign appearances after declaring Saturday that he "cannot defend" Trump's remarks.

The scandal -- just the latest involving his treatment of women -- could not come at a worse time for Trump, who has taken a beating in the polls since his sloppy performance in the first presidential debate September 26.

An average of national polls compiled by RealClearPolitics.com has Clinton leading by 4.5 percentage points.

The two candidates face off starting at 8:00 pm (0100 GMT Monday) at Washington University in St Louis, and will take audience questions in a town hall-style forum.

How much the Trump tape on the one hand, and his accusations against Bill Clinton on the other, dominate the debate is an open question.

- Republican breach -

Clinton may also have to worry about a WikiLeaks disclosure of excerpts from private speeches she gave to major banks in 2013 and 2014.

Although overshadowed by the Trump tape, they show she expressed views in favor of open trade and Wall Street self-regulation to those audiences that are at odds with her positions as a candidate.

Even a winning performance by Trump, however, seems unlikely to mend the deep breach he has opened with many Republicans, alarmed about the scandal's fallout in other down-ballot races.

Notable defectors included Senator John McCain, the 2008 Republican presidential nominee. Dozens of other Republican lawmakers and governors have disavowed Trump's candidacy.

Some leading Republicans called on Trump to quit the race, but he vowed he would never step aside, and legal experts said removing him from the top of the ticket would be extremely difficult.