Donald J. Trump, after weeks of self-inflicted damage, has seen support for his candidacy in national polls dip into the 30s — Barry Goldwater and Walter F. Mondale territory — while Hillary Clinton has extended her lead to double digits in several crucial swing states.

Time to declare a landslide, right? Not so fast.

The vote may be more favorable to Mr. Trump than the worst-case-scenario prognosticators suggest for a very simple reason: Landslides do not really happen in presidential elections anymore.

It has been 32 years since a president won the popular vote by a double-digit percentage. That was when Mr. Mondale suffered an 18-point defeat to Ronald Reagan in 1984. It was also the last time there was a landslide among states, with Mr. Mondale winning only Minnesota and the District of Columbia.