Russia’s support of Mr. Assad has put it on the opposite side of the Syrian conflict from the U.S.

Catch up: Mr. Trump’s decision, announced on Wednesday over the objections of his military and civilian advisers, fulfills the president’s frequently expressed desire to bring troops home. But it also cedes control of Syria to Russia and Iran, and it abandons America’s Kurdish allies.

News analysis: Mr. Trump doesn’t believe that U.S. forces can alter the strategic balance in the Middle East, a view shared by his immediate predecessor, Barack Obama, our national security correspondent writes.

From Opinion: “The Islamic State has not been ‘defeated’ — and our mission in Syria has not been fully accomplished,” two counterterrorism officials in the Trump and Obama administrations write.