We’re not yet halfway through Donald J. Trump’s term as president and already I feel compelled to wonder about a critically important historical element.

How in the name of presidential history are historians going to assess the time that Trump served as president of the United States.

Whether this man finishes his term and — God forbid! — wins re-election to a second term in 2020, I feel confident in asserting that historians must toss out all the standard metrics in assessing Trump’s impact on the nation.

He has managed in just less than two years to enrage our allies, give comfort to some of our adversaries, insult politicians around the world and in this country, use Twitter as his primary vehicle to convey U.S. government policy, launch a worldwide trade war, bust the federal budget with a tax cut, enable hate groups to feel more emboldened than they have in decades.

How will historians judge this individual’s presidency?

He took office after campaigning on a pledge (mostly unspoken but understood all the same) to throw out the standard playbook. I would rate that as the campaign pledge to which he has been most faithful.

Accordingly, those who make their living writing tomes and white papers analyzing the historical significance of major political figures will have to toss their own standard operating procedures into the crapper.

There will be plenty of caveats to attach to this guy’s presidency. There will be the nature of his razor-thin victory — which he keeps describing as “historic” and “record-breaking”; there will be the special counsel investigation and whatever findings it produces regarding collusion and obstruction of justice; there will be the extraordinary number of key Trump aides and Cabinet officers who’ve either been indicted, fired or resigned under pressure.

Just as President Bill Clinton’s obituary will include the term “impeachment,” I feel that Donald Trump’s obit will have some mention of all the ethical and potentially legal troubles that have followed him into the White House.

I’m left to wonder, too: Who will portray Donald Trump when they make a movie about this guy’s presidency?

Presidential historians are going to earn their grant money — bigly — when they sit down to write the book on the 45th president.