Donald Trump, after weeks of self-inflicted damage, has seen support for his candidacy in national polls dip into the 30s — Barry Goldwater and Walter 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 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 Mondale suffered an 18-point defeat to Ronald Reagan in 1984. It was also the last time there was a landslide among states, with Mondale winning only Minnesota and the District of Columbia.

There are a variety of factors that are likely to prevent a candidate today from rallying the huge, 60-plus-point majorities that swept Franklin D. Roosevelt into office in 1936, Lyndon B. Johnson in 1964 and Richard M. Nixon in 1972.

The country is too fragmented and its political temperature too overheated for any single person to emerge as a consensus choice for anything nearing two-thirds of the electorate. And that climate has led the political parties to become far more ideologically uniform than they used to be.

“The biggest difference between today and say, 1936 or 1964, is the composition of the two parties,” said Jonathan Darman, author of the book “Landslide: LBJ and Ronald Reagan at the Dawn of a New America.” Party identification used to be more fluid, making it less difficult for partisan voters to conceive of supporting someone of the opposite affiliation.

“The Republican and Democratic parties were much more heterogeneous than the parties we have today,” Darman added. “Party identification had a lot more to do with regional ties and family traditions than ideology.”

Data show just how much less likely crossover voting is today. Ninety percent of Republicans and two-thirds of independents see Clinton unfavorably, according to the most recent McClatchy/Marist poll. And many Trump defectors are choosing to vote for third-party candidates, which has also contributed to Clinton’s inability to break the 50 percent threshold in most national polls. (All together, the third-party candidates are approaching 15 percent of the vote, indicating an unabated dissatisfaction with the nominees for the two major parties.)

According to Amy Mitchell, director of journalism research at Pew Research Center, about 20 percent of voters now hold political beliefs that place them at the ideological poles of their respective parties — a number that doubled from 2004 to 2014. And these people tend to reinforce one another’s views.

“Those on the ends of the political spectrum are more likely to surround themselves with people that think like they do,” Mitchell said.

This high level of polarization could contribute to a curious electoral phenomenon, which could cost Clinton support: If people begin to believe that she is going to run away with the election, they may lodge a protest vote against her simply to deny her a commanding victory.

“If it becomes a ‘free vote,’” said Peter Hart, a Democratic pollster, “I think that could be one of her problems. If it looks all too easy and all too comfortable, there may be voters who will say, ‘I don’t want her to win by a landslide.’”

If Clinton performs well enough, she could achieve something her husband, Bill Clinton, never did: winning a majority of the popular vote. But given the polling today, the election is showing certain resemblances to the 1992 race that sent Clinton to the White House the first time. That year, many voters dissatisfied with President George Bush flocked to the independent Ross Perot, and neither Bush nor Bill Clinton came close to a majority.

Bill Clinton took a whopping 370 electoral votes, despite winning just 43 percent of the vote. With Perot on the ballot again in 1996, Bill Clinton won only 49 percent.

President Barack Obama’s victory in his first term was considered about as large a landslide as possible given how split the country is. But when compared with the Johnson, Roosevelt and Reagan landslides, it was paltry: just 53 percent. Recent elections were more closely divided. George W. Bush received 48 percent in 2000 — after he failed to win the popular vote but won the Electoral College — and 51 percent in 2004.

The margin of victory, however, is about more than just bragging rights. If voter unease does not subside, a smaller victory could limit Clinton’s ability to claim the kind of popular mandate that she and Democrats on Capitol Hill would like.

“A mandate is some kind of issue platform that you have advocated that is the basis of your victory,” said Lee M. Miringoff, the director of the Marist Institute for Public Opinion. “Not fear of the person who got beaten, which I think is the prime motivator of the Clinton people: the fear of Trump. The same thing can be said for Trump voters: fear of Clinton.”

Absent a popular vote landslide, the only overwhelming chances for victory lie in the Electoral College. Obama won in 2008 with 365 electoral votes to Sen. John McCain’s 173, for example.

Clinton could approach or even exceed that if Trump’s poll numbers remain depressed. But even so, for Trump not to carry close to 20 states would be a defeat on a huge scale. McCain won 22 states in 2008. And despite the scale of that defeat, it was still far less lopsided than Mondale’s one state and the District of Columbia.