With the 2020 presidential contest increasingly looking like a matchup between Senator Sanders and President Trump, the pundits are divided over the expected outcome.

“Trump has an excellent chance to win re-election,” David Leonhardt reassures readers of the Times. “The evidence doesn’t back Democrats’ panic that Bernie can’t win,” Jim VandeHei writes at Axios.

I’m past “who will win” and on to the question of “how big a victory landslide can Trump expect?”

In 1984, President Reagan was re-elected by a 525 to 13 electoral vote margin, with Vice President Mondale carrying only Minnesota. In 1972, President Nixon won reelection by 520 to 17, with Senator McGovern carrying only Massachusetts.*

At the moment, it’s as if Mr. Trump is likely to fall short of a Reagan- or Nixon-level landslide. That’s despite the fact that Mr. Sanders, a 78-year-old socialist from Vermont, looks like a weak opponent. An incumbent president hasn’t lost a re-election bid since George H.W. Bush was defeated in 1992.

A northeasterner hasn’t won the presidency since John F. Kennedy (no, the Bushes don’t count). Governor Dukakis, Secretary Kerry, Governor Romney — they all lost. Plus, Mr. Trump has the tailwind of relative peace and prosperity.

The Trump campaign’s current thinking, political events it has scheduled suggest, is focused on states Mr. Trump won last time around — Michigan, Wisconsin, North Carolina, Georgia, Florida. The Republican convention will be at North Carolina. Potential pickups where events are scheduled include Colorado and Virginia.

If Mr. Trump holds all the states he won last time around, including Pennsylvania, and adds Colorado and Virginia, he’d wind up with 326 electoral votes. That’s nowhere near Reagan- or Nixon-landslide level; it’s even short of President Clinton’s 1996 victory over Senator Dole. It’s in the neighborhood of President Obama’s victory in 2012.

Mr. Trump’s campaign has been paying to air television commercials and has had in-person rallies in Nevada and New Hampshire, which Hillary Clinton won in 2016. It’s hard to tell, though, whether he considers those states, with an additional 10 electoral votes, real pick-up opportunities, or whether he was just counterprogramming the New Hampshire primary and Nevada caucus.

No Republican has carried California in a presidential election since President George H.W. Bush in 1988. No Republican presidential candidate has carried New York since Reagan in 1984. Census data indicate that these two states, with 84 electoral votes between them, have the highest percentage of foreign-born population.

Reagan was a popular former governor of California, and Nixon was also a Californian. Since the Reagan era, because buying television ads in New York and Los Angeles is so expensive, Republicans have mostly given up on even competing for the presidency in the nation’s two largest cities.

President Trump’s decision to sign legislation to end the federal income tax deduction for state and local taxes hit high-tax New York and California especially hard, suggesting he views them as political enemies to be punished rather than potential voters to be wooed. Mr. Trump has since moved his own official residence to Florida from New York.

Polls showing Mr. Sanders beating Mr. Trump are mostly of registered voters, not likely voters, a smaller group that usually tilts somewhat more Republican. Mr. Trump and his allies have yet to unleash what will likely be a wave of advertisements featuring Democrats denouncing Mr. Sanders as extreme, with Hillary Clinton saying, “Nobody likes him, nobody wants to work with him, he got nothing done.”

In any event, returning to Reagan or Nixon-era margins would require a Republican comeback in New York and California. As a political matter, it would be a worthy project for Trump’s second term, requiring policy adjustments on the immigration or tax fronts.

New York has lost congressional seats and electoral votes, and California’s growth has slowed, but the two states still loom large in business and culture. Until some Republican politician, Mr. Trump or someone else, repairs relations between the party and those two big states, Reagan-scale landslides will be impossible to reproduce.

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*Messrs. Mondale and McGovern also carried the Columbia District.