I’ll admit to not knowing anything about Brett McGurk . . . until today.

That’s when I learned that our nation’s leading envoy in the fight to eradicate the Islamic State has decided to quit early. He is angry with Donald J. Trump’s decision to pull out of Syria, to abandon the fight against ISIS in that country. It was a decision that prompted Defense Secretary James Mattis to quit.

Now it’s McGurk who’s hitting the road.

This is a big deal, too.

McGurk had planned to leave in February, but decided to submit his resignation to Secretary of State Mike Pompeo.

McGurk joined the George W. Bush administration and stayed on through the Obama administration, where he was appointed to his current post.

Two years into the Trump administration, McGurk seems to have had enough.

As NBC News reported: Trump’s decision left McGurk flat-footed, unable to explain to U.S. allies who have been fighting ISIS with the United States why they were neither consulted nor informed in advance. Nor have senior Trump administration officials been able to tell allies and Kurdish forces whether U.S. air strikes will continue in Syria to support the mission against ISIS.

Mattis was quite clear in his resignation letter that part of where he differed with Trump is in the treatment of our allies. They cannot trust us to be faithful to our pledges and commitments.

Neither can key administration operatives who are charged with doing the most serious work possible. In McGurk’s case, it is the task of working with allies in the fight to defeat the monstrous terrorists known as the Islamic State.

The chaos is showing signs of taking a terrible toll on U.S. influence in a world that has grown accustomed to what we once touted as our national indispensability.

No longer can we make that make assertion.