He cites as particularly damaging recent comments by Rex Tillerson, the secretary of state said that the "longer-term status of President Assad will be decided by the Syrian people", backing off Barack Obama's initial rallying cry that "Assad must go."
The Turkish Foreign Minister Mevlut Cavusoglu is also pushing that line.
"Idlib attack is a crime against humanity," he tweeted. "Those saying Syrian people will decide Assad's future: no people will remain if attacks continue.
Tillerson's statement was amplified last week by the UN Ambassador Nikki Haley, who confirmed that Assad's removal was no longer a US priority.
In fact, that's been the case for a long time.
Obama's policy on Assad evolved, shaped by Russia's entry into the war on the side of the Syrian regime, and by his administration's growing focus on the fight against the Islamic State group. "Everything is done through a counter-terrorism lens," a US official who worked closely with these issues told me in December. "Would they like Assad to go away? Yes, but only if they feel that wouldn't undermine US interests as they define it."
Given these realities, Obama's Secretary of State John Kerry concentrated on what he thought was achievable - de-escalating the violence and getting some sort of political process off the ground in co-ordination with the Russians.
He crystallised this quiet policy shift in December 2015, when he accepted Moscow's demand that Assad's fate be determined by his people.
Noting that the removal of the president was a "non-starter" as a pre-condition for talks, he said the focus was on facilitating a peace process in which "Syrians will be making decisions for the future of Syria".
Yes, but there's a difference.
The Obama administration, especially Kerry, continued to emphasize that Assad was responsible for the bulk of the violence in Syria, that his brutality fed the extremism that spawned the Islamic State group, and that there could be no peace if he continued in power.
Donald Trump, on the other hand, has been ambivalent, very publicly washing his hands of the issue.
He's endorsed Russia's support of the Syrian leader as producing a team that can fight IS militants, and stated that the US has "bigger problems than Assad".
His anti-IS policy is the clear priority, propelled by the military campaigns in Mosul and Raqqa.
Meanwhile his review of overall Syria policy, including the political negotiations, languishes on the back burn
To what degree, if any, Trump has contributed to Assad's sense of impunity will remain a matter of debate.
But the chemical attack has exposed the disconnect in his policy.
It demonstrates that Assad and the civil war cannot be neatly separated from the battle against Islamic State militants, and highlights the importance of investing diplomacy in a political solution to resolve the conflict.
The atrocity has triggered tough rhetoric and vague threats of action from the White House.
The president said it had changed his view of Assad and Syria. He warned that the regime had crossed a line, although he didn't say if it was a red one.
But a recent statement by his UN ambassador was a more candid sign that this administration is beginning to appreciate the nature of the problem with which Obama and Kerry long wrestled.
"I think the dilemma everyone has," Nikki Haley said," is how do you deal with a government that we wish wasn't there… It's a hard answer, no matter which way you look at it."
It seems the attack has at least focused minds on the question.