Trump was widely criticised after announcing a full withdrawal of US troops from Syria last month, with opponents and even some allies saying it could allow Islamic State to rebuild as well as leaving US-allied Kurdish fighters vulnerable to a Turkish invasion.
But the US president used his speech in New York to claim that the IS leadership was running scared in the wake of Baghdadi's death in a raid in the northwestern Syrian province of Idlib on October 26.
"Just a few weeks ago, American special forces raided the ISIS compound and brought the world's number one terrorist leader to justice," he said. "Thanks to American warriors, al-Baghdadi is dead, his second in charge is dead, we have our eyes on number three."