What if on New Year’s Trump — instead of tweeting “Happy New Year to all, including to my many enemies” who “lost so badly they just don’t know what to do” — had tweeted: “Happy New Year to every American — especially to Hillary Clinton and her supporters who fought a tough campaign — very tough. Let’s together make 2017 amazing (!!!!!!) for every American. Love!”

What if, after a cast member of the musical “Hamilton” appealed to Vice President-elect Mike Pence to “uphold our American values” and “work on behalf of all of us,” Trump — instead of denouncing the actor as being “very rude and insulting” and claiming he “couldn’t even memorize lines” — had instead tweeted: “To the cast of Hamilton: Appreciate your sincere concern for our country. When I am in the room where it happens, good stuff will happen. I will not throw away my shot to work on behalf of all of us!!!”

What if Trump — instead of calling Senate Minority Leader Chuck Schumer “head clown” — had tweeted: “Chuck, you are THE MAN!!! Top Democrat now that Obama’s gone!!! You love to deal. Send me your best health care experts and we’ll fix this thing together in 24 hours, so every American gets better, cheaper care. We’ll both be heroes (well, me just a little bit more). Call me!!!”

That is the sound of magnanimity. It would have generated a flood of good will that would make solving every big problem easier. And it would have cost Trump nothing.

I’ve noted before that one of my favorite movies is “Invictus,” which tells how Nelson Mandela, when he became South Africa’s president, built trust with the white community. Shortly after Mandela took power, his sports advisers wanted to change the name and colors of the country’s famed rugby team — the almost all-white “Springboks” — to something more reflective of black African identity.

Mandela refused. He told his black aides that the key to making whites feel at home in a black-led South Africa was not uprooting all of their cherished symbols. “We have to surprise them with restraint and generosity,” said Mandela.

Most Americans are good-hearted people who are actually starved to feel united again. Many who voted against Trump would have given him a second look had he surprised them with generosity and grace. He did just the opposite. Sad.