“We have defeated ISIS in Syria, my only reason for being there during the Trump Presidency.”

So said Donald J. Trump this morning via Twitter as he signaled a planned withdrawal of about 2,000 U.S. troops from Syria.

I am dubious of this declaration of victory. My concern is as it has been throughout the war on terror, which commenced after 9/11. It is that a declaration of victory is a tenuous proposition at best.

The Islamic State is not — as President Obama infamously described it — the “junior varsity” of terror organizations. ISIS is the real thing. They are monstrous murderers who have, along with al-Qaida, perverted a great world religion and used it to justify their horrendous attacks on fellow Muslims, let alone against Christians and Jews.

To suggest that we can declare categorical victory in the fight against ISIS is risky in the extreme.

How will we respond if ISIS launches another hideous attack in Syria after we have left? Do we send the troops back in?

The president has gotten some push back from congressional allies, such as Sen. Lindsey Graham, R-S.C., who called a U.S. withdrawal from Syria “a big win for ISIS.” He said pulling out prematurely would be an “Obama-like mistake.”

This war against terror cannot possibly be concluded the way “conventional wars” have ended, with someone on one side surrendering and then signing documents signaling the end of a conflict.

I don’t yet know how you determine whether you’ve eradicated the last known terrorist from any battlefield. I just fear we haven’t accomplished that mission in Syria, or anywhere else.