You do not need a statistical model to know that Donald Trump is in a lot of trouble.

His chances were already in jeopardy heading into the second presidential debate Sunday. Hillary Clinton’s lead has grown steadily over the past two weeks, and she was ahead by 5 to 6 percentage points before a videotape revealed Trump bragging about groping women and getting away with it because he’s a celebrity.

Now it’s fair to wonder whether he’ll drag down the whole Republican Party.

The timing could not be worse for Trump. Absentee voting is underway in many states, and in-person early voting is about to start in Ohio and North Carolina.

Even if the revelations did no damage to Trump’s standing, they would still be big trouble. With one month to go and his current polling deficit, Trump can’t afford to tread water.

He had only an 18 percent chance to win the election Friday morning before the videotape’s release, according to The Upshot’s model, with that number set to shrink almost daily unless could Trump could make inroads.

Now, of course, it is very easy to imagine how he sinks farther as a result of the new video.

In the history of October surprises, it is hard to think of anything comparable at this stage of a presidential race. Obviously, it is too early to say exactly what effect it will have on Trump. But the videotape fits all of the major criteria for a damaging scandal, and it puts congressional Republicans in a precarious position.

>> It fits the Democrats’ contention that Trump is a misogynist. The Clinton campaign has been laying the groundwork for weeks with ads about his statements about women.

>> The scandal is easy to explain and can be turned into new television advertisements, although in this case it is probably unnecessary.

>> It is bad enough to force condemnation from Republican officials, and even some abandonments. Very few are defending Trump, ensuring one-sided media coverage and making it easier for Republican-leaning voters to break away as well.

Perhaps Trump will escape a knockout blow, as he has so many times before. Perhaps he will have a spectacular debate performance Sunday night. But the potential downside for Trump and his party is huge. He could lose by a wide margin and endanger the Republican hold on the House at this late stage (although that result is still unlikely).

To be clear, those are worst-case scenarios. They are not inevitable and could even be reversed. But at this point, it is worth looking at the precedents for how things could get out of hand for Trump and his party.

Todd Akin

In August 2012, Claire McCaskill and Todd Akin were in a competitive U.S. Senate race in Missouri before Akin, the Republican candidate, said that victims of what he called “legitimate rape” very rarely became pregnant.

Republican officials from all over the country condemned him and called on him to step aside. The national party offered him little to no support over the last few months of the race.

He lost to McCaskill by 16 percentage points, 55 percent to 39 percent, in a state Mitt Romney won by 9 points. Overall, he lost about 20 percent of the voters who supported Romney, according to exit polls.

Like Trump’s remark, Akin’s comments about legitimate rape played into a narrative, were fit for television advertisements and triggered mass condemnation from Republican officials.

Akin’s collapse — he was basically reduced to the Republican base vote — is a reminder of just how far candidates can fall once their party abandons them.

Mark Foley

In late September 2006, it looked as if congressional Republicans might just survive. The last month or so had gone fairly well for them. The number of competitive seats listed in the Cook Political Report ticked down, and the huge Democratic advantage in the generic ballot shrank. There was a sense that the Republicans could hold on to the Senate and the House if the last six weeks went like the previous six.

Then came Mark Foley. In late September, it was revealed that Foley, a Republican congressman, had sent lewd messages to former congressional pages. At least some House Republicans were aware of it and didn’t do anything. The GOP’s standing in the polls collapsed, the Democratic wave built quickly, and Republicans in safe districts soon found themselves in jeopardy.

The similarities between the Foley scandal and Trump’s are a little more superficial than those between Akin and Trump. What’s most striking is that the prelude feels similar: Like the Republicans of 2006, the Republicans of 2016 had a pretty decent stretch from mid-August to late September. The underlying vulnerability in each case — George W. Bush and Trump — did not go away. But it really seemed as if the 2016 GOP could dodge the worst of it. Perhaps Trump would lose by only a modest margin, and the Republicans could hold the Senate. In the end, the worst-case scenario hit, and hit abruptly.

In some ways, the link between Foley and the conduct of the rest of the Republican House was clearer in 2006: House Republican leaders were aware of his behavior, and Democrats had already been running against a Republican “culture of corruption.” This year, Democrats have not quite laid the groundwork to tie Republicans to Trump — although they could still try to do so, especially with Republicans who continue to support him

But Trump poses a more difficult challenge for Republican officials than Foley did: There was no cost to repudiating Foley, but the decision on whether to repudiate Trump puts Republicans in the unenviable position of alienating either Trump’s fervent base or moderate voters. It’s difficult to predict how this dynamic will play out — it will probably vary by state and by candidate.

My guess is that even this worst-case scenario would leave the Republicans in control of the House, although narrowly. Even a 31-seat gain for the Democrats like the one in 2006, for instance, would barely be enough to put the Democrats over the top this year (they need 30). But this year, the Democrats won’t have so many opportunities to win seats held by Republicans embattled by scandal, including Foley’s own seat.And this year’s political environment is not as favorable for Democrats as it was then.

As the Foley scandal makes clear, however, there’s a lot of downside for Republicans, and it’s not too late for a whole host of Republican-leaning districts to become much more competitive.

© 2016 The New York Times Company