Andrew Cohen is author of Two Days in June: John F. Kennedy and the 48 Hours That Made History. He is a Fulbright Scholar at the Woodrow Wilson International Center in Washington.

On the morning after he won the presidency in 1968, Richard M. Nixon met reporters to declare victory and do what winners do after bruising elections: make a plea for unity.

Nixon recalled signs he saw whistle-stopping in Ohio. "The one that touched me the most was a teenager [who] held up the sign, 'Bring us together,' " he said. "And that will be the great objective of this administration, at the outset, to bring the American people together."

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His promise came after a season of assassination, race riots and anti-war marches. America was traumatized. Nixon defeated Hubert H. Humphrey by a narrow 500,000 votes.

On the morning after his election this week, Donald Trump also met the media to declare victory over Hillary Clinton. Suddenly this demagogue was a conciliator, soft and gracious, promising unity and perhaps a little irony, too.

"Now it's time for America to bind the wounds of division," he said. "We have to get together. To all Republicans and Democrats and independents across this nation, I say it is time for us to come together, as one united people. It's time."

Mr. Trump, like Nixon, was offering the statutory postelection declaration. It's an expression of atonement on the morning after for the sins of the night before. Now he said that representing "all Americans is important to me." (Curiously, he used the same phrase in the first debate when he promised to call his rival "Secretary Clinton." He soon reverted to "Hillary," preceded by "lying", "nasty" or "crooked.")

Like Nixon and most new presidents, Mr. Trump isn't serious about bringing people together. Conciliation mattered to Abraham Lincoln in 1861, Gerald Ford in 1974 and Barack Obama in 2009, but today it's as hollow as a coreless apple. When it comes to unity, presidents preach multiplication but practice long division.

Mr. Trump ran a mean, cynical campaign as a white nationalist, disparaging immigrants, degrading women, mocking the disabled, using coded anti-Semitism. When President Obama praises Mr. Trump's victory these days, as he must, you have to think: 'Come on, man!"

Mr. Trump didn't blow the so-called dog whistle in his campaign; he sounded the trumpet. He called Mexicans "rapists and murderers" and Muslims "terrorists." Unity? Mr. Trump is less Nixon than George Wallace, the southern racist who also ran, as an independent, in 1968.

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Even if president-elect Trump wants to unite a polarized people, it won't be easy. He won only 47 per cent of the popular vote (making him a minority president) with 200,000 fewer votes than Ms. Clinton.

If Mr. Trump won the election stoking fear and anxiety – crime is rising, terrorists are coming, industry is leaving, drugs are spreading – then why bother with the unity card? Divide and rule is more effective.

But if he is conscious of the moral burdens of the presidency, and is serious about bringing unity to a country in a continuing cultural war, here is what he can do:

Appoint Democrats to senior cabinet posts, as John F. Kennedy named prominent Republicans. Mollify Democrats in the Senate, as Ronald Reagan did; otherwise they can filibuster legislation and obstruct judicial and diplomatic nominees.

Seek compromise on immigration. Amend rather than repeal Obamacare. Forget prosecuting Ms. Clinton, building a wall with Mexico and deporting 11 million undocumented aliens.

Apologize for the harsh rhetoric. Show humility, and contrition, too.

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Mr. Trump should do all this but he can't. Temperamentally, he is about winning. Politically, he is not apt to compromise, nor will his circle of advisers – Newt Gingrich, Chris Christie, Rudy Giuliani – encourage that. Triumphalist Republicans, led by a newly empowered Vice-President Mike Pence, will push a social conservative agenda, not consensus-building.

Nixon, for his part, had no interest in unity. He escalated the war in Vietnam. He harassed critics. Ultimately, though, he managed a perverse unity: when he was driven from office in 1974 for his treachery, the whole country cheered.

Nixon saw unity as a useful delusion. One of his speechwriters suggested later that that sign in Ohio had been contrived. Nixon never saw it but knew what presidents had to say, even if he didn't mean it.

Mr. Trump doesn't either – and this country will remain as divided in four years as it is now.