To Damascus, this looked like a green light to show Syrian civilians and rebels that there were no limits to what the regime would do to win, that the government could kill by whatever means to get the job done most quickly. Mr. Assad believed this not because he is insane or reckless, but because the United States convinced him that it was true.

He must have been just as surprised and confused as the rest of us on Friday when Tomahawk cruise missiles began landing in the first direct United States attack against the Assad regime in six years of war.

Overall, the strike will probably have only a limited impact. Mr. Assad’s forces still have the upper hand. True, the Trump administration’s decision to take out a Syrian Air Force base signals a shift: The Assad regime cannot do whatever it pleases, use whatever weapons it thinks will bring it victory fastest. But that doesn’t mean the United States is necessarily ready to forcefully intervene to change the course of the conflict.

Mr. Assad will be shaken, but he now has a better sense of his limits and strengths. On one hand, Iran and Russia failed to defend him. Many analysts had warned that American military action in Syria would set off World War III, but Russia has so far responded with only words. On the other hand, Mr. Tillerson quickly made clear that the cruise missile strikes do not signal a change in American policy — so far there is no immediate plan to force Mr. Assad’s ouster, to protect the opposition or to establish safe zones in Syria.

The Assad regime will return to waging its war, with Russian and Iranian backing. If Mr. Assad is smart, he will do it without chemical weapons — siege, starvation and barrel bombs will remain his tools of choice. The United States has finally showed it will act against the regime under certain circumstances, but it hasn’t declared any new rules of the game. Unless it decides the violence in Syria, chemical or otherwise, must end, Mr. Assad will still be determined to win.