The regime’s return to all-out state terror then, featuring collective punishment on a massive scale, doomed peace negotiations in late 2013 and early 2014. Stepped-up, unopposed mass homicide contributed decisively to the migrant crisis that swept through Western Europe in 2015, a development whose political effects on democracies delighted the Kremlin no end.

Key elements of the same sequence are unfolding now. Assad and his external supporters—Russia and Iran—calculate that they can inflict death and destruction in densely populated residential neighborhoods to whatever extent they please, provided they do so without sarin gas. Noticing that yet another American president has drawn a chemical weapons red line, Assad has weaponized chlorine gas and has used it to enhance the element of terror among parents and their children. He and his enablers are taking the measure of another American administration.

The administration’s response? Here are the words of H. R. McMaster, President Trump’s national-security adviser, spoken at the Munich Security Conference just days ago:

In April of 2017, when the Assad regime again used these heinous [chemical] weapons against innocents, the United States responded. We acted to deter future chemical attacks and to ensure that the use of these weapons never again became routine. Public accounts and photos clearly show that Assad’s chemical weapons use is continuing. It is time for all nations to hold the Syrian regime and its sponsors accountable for their actions and support the efforts of the Organization for the Prohibition of Chemical Weapons.

It is a remarkable statement: a public admission of failure. The April 2017 cruise missile strikes were intended to deter future chemical attacks. Yet “Assad’s chemical weapons use is continuing.” What to do about it? Hold the regime and its sponsors “accountable”? By supporting the efforts of a body whose good works were undermined by the Assad regime’s duplicity? Who will compel compliance?

Soon after the April 2017 retaliatory strikes were completed, I urged the administration to lodge the following statement (or something like it) with Russia: “This time we struck because your client used sarin. Next time it may be in response to a different instrument of terror. Mass homicide is inadmissible. It encourages extremists, it undermines our allies, it obstructs the peace talks you say you want, and yes: It targets innocent men, women, and children. We reserve the right to strike when and where we choose if the mass murder continues. Get your client out of this filthy business.”

Sadly, this message seems not to have been passed. Imagine being a parent in Eastern Ghouta and praying to God that the regime uses sarin gas so that someone will be inspired to do something beyond talking about the horror of it all. To read the statements of United Nations Ambassador Nikki Haley about this abomination is to experience the reality of governmental continuity, notwithstanding a change of administration. She is approaching the eloquence of her predecessor, Samantha Power, on these matters.