WASHINGTON — YOU know how desperate President Obama is — as he contemplates all his accomplishments going down the drain at the hands of a man he has total contempt for — when he is willing to do something so against his nature.

He tried to persuade Donald Trump.

We saw that unicorn glimpsed only fleetingly in the last eight years: the cajoling Barack Obama.

The president flattered the president-elect by letting Trump rack up the ego arithmetic.

“This was a meeting that was going to last for maybe 10 or 15 minutes and we were just going to get to know each other,” Trump told reporters afterward, as they sat in front of the Oval Office fireplace. But, he marveled, “The meeting lasted for almost an hour and a half.”

And lo and behold, it worked — sort of. In his first post-election newspaper interview, Trump told The Wall Street Journal that he would consider leaving in place the parts of Obamacare that allow children to stay on their parents’ health plan until they are 26 and that prevent people from being refused insurance because of existing conditions.