“I am scared that if Ronald Reagan gets into office, we are going to see more of the Ku Klux Klan and a resurgence of the Nazi Party,” Coretta Scott King said in November, 1980. “I’m afraid things are going to blow sky high during this next term,” a nursing student said. He’s a “nitwit,” added a Democrat. “He’s shallow, superficial and frightening,” one of that year’s historic numbers of “undecideds” insisted.

Ronald Reagan “seems not to relish complexity and subtlety,” the New York Times editorial endorsing President Jimmy Carter’s re-election proclaimed. “The problem is not a loose lip but the simple answer.” While fearing what Reagan’s own running mate, George H.W. Bush, had dismissed as Reagan’s “voodoo economics” during their primary fight, the editorial board feared “voodoo diplomacy,” too.

From coast to coast, half of a divided nation abhorred — and underestimated — the president-elect. “The American people,“ Hamilton Jordan, a key Carter aide, said, “are not going to elect a 70-year-old, right-wing, ex-movie actor to be president.”

Pollsters reported in 1980 that “More voters held negative attitudes toward each presidential candidate than in any campaign since polling began” — a record we just broke in 2016. The economic dislocation of galloping inflation and the energy crisis produced a nasty campaign. Feeling neglected by Washington, millions embraced Ronald Reagan’s populism.

Despite the Democratic panic, Ronald Reagan left America richer and safer after two terms as president. Reagan defied expectations by turning toward the center. He acted as president of the United States, not president of the Republican Party. Reagan used the transition period to heal wounds while claiming a broad policy mandate, despite winning only 50.7 percent of the popular vote. He vowed to “rebuild a bipartisan base for American foreign policy.”

His cabinet choices were so moderate that Pat Buchanan, the conservative flamethrower whose rhetorical bluster anticipated the advent of Donald Trump, lamented: “Where is the dash, color, and controversy — the customary concomitants of a Reagan campaign?” Just weeks into Reagan’s first term, conservatives were demanding that his aides had to “Let Reagan be Reagan,” meaning: stop being so reasonable.

But in adjusting, in tempering, Reagan was being Reagan. He knew the Constitution limited presidential powers — and he faced a Democratic Congress led by the formidable speaker of the House Tip O’Neill to remind him further. Illustrating Richard Neustadt’s lesson that the power of the president is mostly “the power to persuade,” many of Reagan’s achievements were symbolic. Rather than shrinking government as he promised, for example, he only lowered the federal government’s growth rate.

History is not destiny. And Reagan had both a lighter touch than Mr. Trump, and eight years’ experience as governor of California. Still, history is full of shifts and surprises. Mr. Trump must be a healer and unite America, as he tried doing in his victory speech. If he fails, the checks and balances that sometimes help crusading ideologues become effective leaders can ultimately impose a necessary gridlock.

When asked about conservatives’ frustration with him, Reagan kindly insisted it was only a “very few” critics. He said: “There are some people who think that you should, on principle, jump off the cliff with the flag flying if you can’t get everything you want.” Reagan recalled that “If I found when I was governor that I could not get 100 percent of what I asked for, I took 80 percent.” So far, Mr. Trump, the political amateur and sputtering demagogue, has lacked Reagan’s magnanimity or his flexibility. Can the reality-show star turned president-elect mimic the actor turned president?

Gil Troy is a professor of history at McGill University and the author of “Morning in America: How Ronald Reagan Invented the 1980s.”