Iranian military boats have quietly ended years of harassment of US Navy vessels in the Persian Gulf, and it looks like another welcome sign of a new cop on the beat.

For years, armed Iranian “fast boats” would charge at US ships in a dangerous game of chicken, rising to a level the Navy deemed “unsafe or unprofessional” at least twice a month. It was a clear signal of disrespect, and a test of what Washington would put up with.

But the game stopped last summer, the Wall Street Journal reports.

Officially, the Navy doesn’t know why. US Central Command chief Gen. Joseph Votel says, “I hope it’s because we have messaged our readiness . . . and that it isn’t tolerable or how professional militaries operate.”

But Tehran surely takes that “isn’t tolerable” message a lot more seriously now that President Barack Obama is out of office.

Obama, after all, had shown he wouldn’t enforce his own red lines, infamously blinking rather than live up to his own vow that use of chemical weapons by Syria’s bloody Bashar al-Assad would be a “game-changer.”

Plus, he’d proven unwilling to confront Iran over anything, staying silent during the critical early days of the 2009 Green Movement protests and then later giving up the store in negotiating the 2015 nuclear deal.

Not to mention letting Tehran get away with taking two Navy crews hostage in 2016, and ignoring countless other Iranian provocations after striking the nuke deal.

To be fair, Iran might have backed off in the Gulf if Hillary Clinton had won in 2016. But it’s facing President Trump instead: a leader who has enforced Obama’s red line in Syria and overseen the ruination of ISIS, and who’s anything but wedded to preserving the nuclear agreement at all costs.

The fast-growing US economy is far from the only fruit of change in Washington.