WASHINGTON — Just days before his inauguration, President-elect Donald Trump got into a verbal battle with Georgia Rep. John Lewis, one of America’s greatest living heroes and an icon of the civil rights movement.

As all surely know by now, Lewis said that Trump isn’t a legitimate president, to which Trump retorted that Lewis is: “all talk, talk, talk — no action.”

How rich that Trump would be so offended by a charge of illegitimacy when he spent years trying to prove the same about Barack Obama’s presidency.

But Trump doesn’t take an insult lying down, you know; when someone fires at him, he fires right back.

This impulsiveness, once perhaps a quirky habit, can have less amusing consequences in a president whose tweets can upset global relations, or worse.

Domestically, it’s no picnic, either.

Lewis explained that his position was based in part on alleged Russian interference with the election.

As for all talk and no action, does Trump even know who John Lewis is? The man was bludgeoned bloody by police and hospitalized for peaceably crossing the Edmund Pettus Bridge during 1965’s historic civil rights march from Selma to Montgomery. Obviously, Trump was referring to Lewis’ more recent record, but this is hardly the time to start a war with a hero — not that this is his first time. Trump also criticized Sen. John McCain in 2015, saying he was only a hero because he was captured.

Nice touch, Mr. Commander in Chief.

More to the point, his takedown of Lewis is such a waste of time and a squandering of human resources that he may need someday. What profit could there possibly be in firing back at someone so admired by so many, especially within the African-American community? By punching back, Trump stoked an opposition movement among congressional Democrats.

Meanwhile, his meeting Monday with Martin Luther King III on the namesake day celebrating his father’s life seemed like a one-upman’s stunt contrived to show his bona fides among African-Americans. Trump essentially was saying that he didn’t need Martin Luther King Jr.’s wingman when he has King’s son in his pocket. No offense to King III, but there was only one King who led the civil rights movement — and John Lewis was by his side when it counted.

As Inauguration Day looms, one wishes that Trump’s vow “to be so presidential” would start early. Why wait? If a president’s role is in part to unify the country, he can’t start soon enough. Imagine if Trump had taken the high road in this instance. He could have not remarked at all, which would have been refreshing. Or, as suggested in the fake news item above, he could have commended Lewis’ record and expressed hope that he’d soon change his mind.

Trump would have seemed a beacon of wisdom, self-restraint and generosity. And Lewis, who insists he has a moral obligation to stand against Trump’s history of racist and misogynistic speech and behavior, would have been seen as querulous (Lewis also boycotted George W. Bush’s first inauguration), while being dispatched without dishonor.

Instead, Trump’s unnecessary engagement of Lewis has pitted Democrats against Republicans: Do you stand with Trump or Lewis? That’s a helluva choice.

More than 50 Democratic representatives have sided with Lewis and plan to join him in boycotting the swearing-in ceremony and the peaceful transition of power, in effect joining hundreds of thousands of protesters for what promises to be an animated weekend.

This isn’t to suggest that Lewis is necessarily right with the course he has chosen. People will have to decide for themselves if his moral objection to Trump is justified or whether boycotting the inauguration is disrespectful of the office of the presidency. (“Both” is a valid option.)

But there’s only one person who can bring this episode to a gracious close. In my fantasy, Trump issues a statement — 140 Twitter characters, if he must. It would read as follows: “With this, my last tweet until I leave the presidency, I invite Lewis to the Oval Office to find mutual ground in aiding all Americans.”

It’s the big-league thing to do.

Kathleen Parker is a columnist with The Washington Post. Her email address is: kathleenparker@washpost.com.