At least three factions prepare to fight for the party, divided amid Donald Trump's accusations of corruption and his appeals to fading demographics

Accusations of betrayal. Demagoguery and hatred. The bunker in Berlin. Comparisons with Adolf Hitler have been tempting throughout Donald Trump's 2016 campaign for the presidency – never more so than at its mad, destructive climax.

The Republican's presidential bid appears to have become the campaign equivalent of the last days of the reich, when Germany's leadership raged at bearers of bad news from the battlefield, ordered non-existent divisions to launch counteroffensives, and embraced a nihilistic plan to burn it all down and take everyone along.

The difference is, unlike then, there seems to be little awareness of impending defeat or understanding of how it came to be. Instead, attitudes are like those after the first world war when Germans on the far right coined a word for their myth of betrayal: Dolchstoßlegende.

Donald J. Trump (@realDonaldTrump) This election is being rigged by the media pushing false and unsubstantiated charges, and outright lies, in order to elect Crooked Hillary!

Trump is trailing Hillary Clinton badly in national polls, sometimes by double digits. Jubilant Democrats are eyeing so-called "red states" such as Georgia and Utah and expanding their ambitions to take both the Senate and House. The Trump campaign has yanked advertising and staff out of Virginia, and major donors are pulling the plug. The writing seems to be on the wall of polling firms, campaign offices and newsrooms across the country.

"So is this presidential election over?" asked Michael Barone, resident fellow at the American Enterprise Institute. "Almost certainly."

In September, Trump appeared competitive. In October, he collapsed. A 2005 video in which he bragged about groping women was followed by a slew of allegations of sexual assault and more than 160 Republican leaders who abandoned Trump. He has declared war on members of his own party, attacking the House speaker, Paul Ryan, and turned to increasingly authoritarian claims, insisting that Clinton must be jailed.

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Republicans have started to fear that 8 November will not be the end but rather the beginning of all-out civil war, asking whether Trumpism can survive Trump, and whether those who support him can survive his candidacy. Who can unify the party of Abraham Lincoln? Who can avoid a historic fourth consecutive defeat in the election of 2020?

Much depends on whether 2016 has an effect on the Senate, where Democrats stand a strong chance of taking control, and on the House, which may now be in play. The maverick businessman has already threatened to dispute the election's result, claiming the election is rigged, and already lashed out at moderate Republicans for not backing him.

"No one knows what's going to be left of the party on November 9," said Charlie Sykes, an influential conservative radio talkshow host. "Republican officials I've talked to have gone beyond anger to a sense of anguish about the future of the party," he said.

"The damage that Trump has done will not end on November 8. I don't think any Republicans really know what a post-Trump party looks like. They're hoping it's a one-off event but I don't see the civil war going away any time soon."

Sykes, who has known Ryan since he was first elected to the House in 1998, regards the 46-year-old Wisconsin Catholic, a family man and devotee of Ayn Rand, as its intellectual leader. "If there's anybody who ought to emerge as the titular leader of the party in the ruins, it will be Paul Ryan."

Facebook Twitter Pinterest 'If there's anybody who out to emerge as the titular leader of the party in the ruins, it will be Paul Ryan.' Photograph: Tannen Maury/EPA

After the defeat of Mitt Romney – a harsh critic of Trump and Ryan's 2012 running mate – Republican officials produced an "autopsy report" concluding that to win back the White House, the party needed to appeal to young voters, women and minorities.

"They did the precise opposite," Sykes said, noting how Trump had alienated those precise constituencies. "They've got to get grips with the fact that if you want to be a national party you cannot win elections if you do not appeal to women, African Americans and Hispanics and young people."

Instead, Trump's rallies are dominated by largely white crowdswho have embraced his angry, anti-immigrant rhetoric. "The Trump campaign is premised on turning out a part of the American population that's shrinking," said Lanhee Chen, policy director for the Romney presidential campaign.

"For the party to succeed, it needs to focus on the part of the population that's actually growing. I think that challenge is one that can be addressed post-