In this unpredictable election year, the simplest way to assess the state of the race is to check how often Donald Trump complains that the fix is in. Polls can be unreliable and contradictory, most radio and cable news broadcasts are nakedly partisan, but Trump’s fragile ego can be trusted: if he’s whingeing, he’s losing.

Since his trouncing in the first presidential debate, the Republican nominee has again begun to warn of voter fraud. "I hear too many bad stories, and we can't lose an election because of you know what I'm talking about,” he told supporters in Manheim, Pennsylvania, urging them to “monitor” the polls in “certain areas” on election day.

At a rally in 73% white Novi, Michigan, on the outskirts of 83% black Detroit, he said: “Go to your place and vote, and then go pick some other place, and go sit there with your friends and make sure it's on the up and up.”

Democrats are taking the implied threat of voter intimidation seriously. Philadelphia’s former City Manager Joe Certaine told me that his priority in the last month before the vote, now that the deadline for registration has almost passed, is to set up an “election protection mechanism” to protect polling stations from people who “harass and intimidate and otherwise sow confusion on election day”.

In the first batch of national polls since the debate, Hillary Clinton’s lead has bounced back to roughly where it was in early September, before her literal and figurative stumbles, her pneumonia and her “deplorables” comment briefly made it a tied race. CNN has her up 51%-45%, CBS up 49%-43% and Morning Consult 46%-39%. In surveys that include third-party candidates Gary Johnson and Jill Stein her cushion is thinner, but still outside the margin of error at 3.2%.

More importantly, Clinton also leads in almost all the latest swing state polls: by 3.2% in Florida, 7.5% in Pennsylvania, 6.8% in Michigan, 8.2% in Virginia and 1.2% in Nevada, according to the Real Clear Politics average. The one exception is Ohio, where Trump is still 2% ahead.

This is likely to get worse before it gets better for Trump, following what Republican political strategist John Weaver described as “probably the worst week any presidential nominee has had in modern American history.” Weaver is an adviser to Ohio’s Governor John Kasich, and no friend of Trump, but his assessment was widely shared. Former House Speaker Newt Gingrich called it “a lost week, a week which has hurt him, which has shaken his own supporters”.

Trump followed up his incoherent and bad-tempered performance in the debate with a petulant attack on Alicia Machado, the Miss Universe he allegedly called “Miss Piggy” and “Miss Housekeeping” in reference to her weight. He didn’t seem to care that he was walking into a trap set by the Clinton campaign. “She gained a massive amount of weight, and it was a real problem,” he told Fox & Friends, causing his cheerleaders at the breakfast show to wince visibly.

Next came the revelation in the New York Times that Trump almost certainly paid no federal income tax for many years after claiming a $916 million loss on his 1995 return. Newsweek reported that one of his companies violated the Cuba embargo, the Washington Post showed that the Trump Foundation is operating illegally and the Los Angeles Times ran a piece about Trump’s habit of telling managers to fire women he deems unattractive on visits to his properties.

Trump has shown a remarkable ability to bluster his way through scandal after scandal that would have sunk most other political campaigns - “Who else has had more bad stories written about them than me?” he asked rhetorically, when I last interviewed him for the Sunday Herald - but the cumulative effect finally seems to catching up with him.

Among white, university-educated women, a group that favoured Mitt Romney over Barack Obama by 6%, he trails Clinton 57%-27%. He cannot win an election with the votes of white men alone, no matter how overwhelming the margin.

In Colorado on Monday, Trump presented himself as the comeback kid. “When the chips are down is when I’m at my very best,” he said, alluding to a string of business failures in the 1990s. “They said I was finished. Everybody said I was done. I am still here."

If he is to win, his comeback has to start tonight at the second debate. There are several factors working in his favour, chief among them the media’s clear self-interest in a close contest. Expectations could hardly be lower, meaning that he doesn’t have to do much to be judged the winner by pundits.

At rallies, Trump has criticised the first debate moderator, Lester Holt, and complained of a faulty microphone that apparently made him a little hard to hear in the hall (his mic worked perfectly for the eighty-four million people watching at home). This is the closest he can come to admitting that he had a poor night. In Iowa, he boasted that he had won by “a landslide,” despite all evidence to the contrary.

Writing in the New York Post, Rupert Murdoch’s Clinton-hating tabloid, columnist John Podhoretz accused Trump of “vanity and laziness,” adding that “his supporters should be furious with him, and so should the public in general.” Conservative newspapers that have never endorsed a Democrat, such as the Arizona Republic and the Cincinnati Enquirer, have given Clinton their backing.

Four years ago, Barack Obama put in a listless performance at the first debate and saw his lead over Mitt Romney in the polls wiped out, but much improved showings in the second and third debates turned things around. Can Trump do the same?

“So much of this is personality-driven and specific to the individuals involved,” said Political Science Professor Robert Erikson, of Columbia University. “In 2012, after Obama did so poorly in the first debate, he worked very, very hard and re-strategised and listened to the people around him to come back strongly in debates two and three. I really question if Donald Trump is capable of doing that.”

Erikson and his research partner Christopher Wlezien studied polls from every presidential election from 1952-2008 and concluded that there is only “fragile” evidence that debates alter electoral outcomes.

The first televised presidential debate between John F Kennedy and Richard Nixon in 1960 is an exception to this rule. Ronald Reagan and Jimmy Carter’s solitary debate in 1980, a week before the vote, may be another. But otherwise, famous gaffes - Al Gore’s sighing in 2000, Gerald Ford’s bizarre assertion that “there is no Soviet domination of eastern Europe” in 1976, George HW Bush’s neurotic glances at his watch in 1992, and so on - merely served to reinforce existing perceptions.

This is bad news for Trump, who has never led the race. Clinton is an accomplished debater and can play it safe. He has no option but to attack.

Half the questions will come from the moderators - including CNN's main news anchor Anderson Cooper. The other half will be asked by members of the audience, from a list of questions submitted online. “The second debate is a town hall format, which is a real wild card,” said Journalism Professor Alan Schroeder of Northeastern University. “You don’t know how they’re going to engage with each other. We can imagine how Hillary will perform but Donald? It’s going to be a surprise no matter what.”

In the spin room after the first debate, Trump congratulated himself for not bringing up Bill Clinton’s infidelities. He left that to his surrogate, former New York Mayor Rudy Giuliani, who said that if Hillary believed Bill’s denials of a liaison with Monica Lewinsky then she is “too stupid to be president”.

Giuliani, like Trump, has been married three times. Both were caught cheating on their wives. If Trump does decide to go after Hillary for enabling Bill’s behaviour, he leaves himself open to a devastating counter-attack.

The ex-president remains an asset to his wife’s campaign, but he can also be a liability, as he showed in Flint, Michigan, with an improvised riff about the USA’s insane for-profit healthcare system and the Obama administration’s efforts to fix it. The next day, in Arizona, Trump gleefully observed that Bill Clinton had “told the truth” about the Affordable Care Act when he “absolutely trashed” it. Expect that to come up at tonight’s debate.

Trump will presumably raise the terrorist attack on the US Consulate in Benghazi that left four Americans dead during Hillary’s tenure as Secretary of State, although if the Republican-led House Select Committee couldn’t pin anything on her in eleven hours of interrogation, it seems doubtful that he will be able to do so in a few minutes of televised back and forth.

He is certain to bring up Clinton’s use of a private email server in her time at the Department of State. The issue has been litigated in court and in the press for months, but Clinton has not been able to come up with a satisfactory response to the accusation that she put classified information at risk and then tried to cover up her recklessness.

In the first half hour of the first debate, Trump had Clinton on the defensive on the issue of trade and how best to protect American workers from the destructive effects of globalisation. She is sure to have a better retort this time, featuring Trump shirts made in Bangladesh and Vietnam, Trump suits made in Indonesia, Trump glasses made in China and Trump furniture made in Turkey.

Since three pages of Trump’s old tax returns were leaked to the New York Times, Clinton has been hammering him on the campaign trail for shirking his responsibilities. “While millions of American families — including mine and yours — were working hard, paying our fair share, it seems he was contributing nothing to our nation,” she told supporters in Toledo, Ohio.

“That makes me smart” - Trump’s response in the first debate, is unlikely to cut it. In a recent CNN poll, 86% of respondents viewed paying taxes as a “civic duty” and only 12% said they are an “unnecessary burden”. Trump’s line - “I know our complex tax laws better than anyone who has ever run for president and am the only one who can fix them” - will not be easy to defend.

On Tuesday, vice presidential candidates Tim Kaine and Mike Pence met in a debate notable for Kaine’s incessant interruptions and Pence’s determination to discuss his own, straightforwardly conservative platform rather than Trump. Afterwards, commentators determined that Pence had ‘won’ with his steady performance (there are no draws in American sport or politics, only winners and losers) but Kaine had the last word: “He is asking everybody to vote for somebody that he cannot defend.”

Clinton’s re-appearance in Ohio, a state her campaign had all but abandoned, is a sign of renewed confidence that she can match Obama’s sweeping electoral victories. She can afford to lose Ohio and Florida. Trump probably needs both, plus Pennsylvania or Wisconsin, New Hampshire or Colorado. On Thursday, an Emerson College poll in deep Republican red Arizona showed Clinton leading by two points.

The RAND Corporation estimates that around 11% of voters remain undecided. YouGov puts the figure at just 8%. There is still time for an October surprise, but Trump is running out of time. Another disastrous performance at tonight’s debate would finish him.