To North Korea, the strike is a warning that Mr. Trump is willing to match action with his tough tweets warning that the U.S. will not permit Pyongyang to threaten American security by marrying its small nuclear arsenal with intercontinental ballistic missiles capable of reaching our shores. North Korea is also believed to possess chemical weapons which it could reign down on Seoul and American forces stationed near the South Korean capital in the event of conflict.

To China, it shows that Mr. Trump is prepared to make good on his pledge to take unilateral action against North Korea if Beijing is unwilling to pressure its mercurial neighbor into suspending, if not dismantling its own nuclear program.

And perhaps most important, the strike shows Russia that President Trump’s unlikely bromance with Russia’s autocratic ruler Vladimir Putin has its limits, and that Mr. Trump is likely to insist that Mr. Putin stop making excuses for his brutal client and contain Mr. Assad’s most outrageous conduct. Military action which throws Moscow off-balance could not come at a better time for Mr. Trump, whose administration is beset by multiple investigations into whether his campaign officials colluded with Russia in interfering in America’s presidential election and whether such collusion helped elect Mr. Trump over his Democratic rival, Hillary Clinton.