You do not need a statistical model to know that Donald J. 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 last two weeks, and she was ahead by five to six percentage points before a videotape revealed Mr. 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 Mr. Trump. Absentee voting is already 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 Mr. Trump’s standing, they would still be big trouble. With one month to go and his current polling deficit, Mr. 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 Mr. Trump could make inroads.