MOSCOW — If Russia once maintained at least a semblance of distance from President Bashar al-Assad of Syria, it rushed to his defense after the American missile strike ordered by President Trump on Thursday. The attack cemented Moscow more closely than ever to the notorious Syrian autocrat.

Even as the United States condemned Mr. Assad for gassing his own citizens and held Russia partly responsible, given its 2013 promise to rid Syria of chemical weapons, the Kremlin kept denying that Syria had any such capability.

By championing Mr. Assad and condemning American “aggression,” President Vladimir V. Putin of Russia seemed to be burying the idea that he could somehow cooperate with the Trump administration to end the conflict on his terms.

The solidarity with Damascus is likely to cause problems for Russia in the long run, analysts said, although Mr. Putin probably cannot be persuaded to loosen his embrace any time soon.