This photo provided Tuesday, April 4, 2017, by the Syrian anti-government activist group Edlib Media Center shows a Syrian doctor treating a child following a suspected chemical attack in Khan Sheikhoun, Syria. Uncredited AP
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Sen. John McCain, R-Ariz., on Tuesday called Tillerson’s remarks “one of the more incredible statements I’ve ever heard.”

“Bashar Assad and his friends, the Russians, take note of what Americans say,” he said on CNN. “I’m sure they took note of what our secretary of state said just the other day. . . . I’m sure they are encouraged to know the United States is withdrawing and seeking a new arrangement with the Russians. It is another disgraceful chapter in American history and it was predictable.”

It is another disgraceful chapter in American history and it was predictable.

Sen. John McCain, R-Ariz.

Sen. Lindsey Graham, R-S.C., last week called the Trump change in policy “the biggest mistake since President Obama failed to act after drawing a red line against Assad’s use of chemical weapons.”

Shajul Islam, a British doctor on the scene Tuesday, tweeted videos showing a patient with “non-reactive pinpoint pupils” that he said proved the attack was not chlorine. Another doctor on the scene in Idlib, Feras al Jundi, said the attack could only be sarin or a similar deadly agent.

“If it’s what it looks like, it’s clearly a war crime,” a State Department official, speaking on the condition of anonymity, told reporters in a briefing on Tuesday.

Responding to the attack, Sen. Bob Corker, R-Tenn., said the U.S. “figuratively jumped in Putin’s lap over an agreement to remove Syria’s chemical weapons that we now know did not fully occur.”

Sen. Bob Casey, D-Pa., called the chemical attack “continued proof that Bashar al-Assad is a war criminal, not a potential partner.”

House Foreign Affairs Committee Chairman Ed Royce, R-Calif., said in a statement that “it is clear there is no hope for real peace in Syria until Assad is held accountable.”

Many U.S. allies on Tuesday seemed to agree. “Those saying Syrian people will decide Assad’s future: No people will remain if attacks continue,” Turkish Foreign Minister Mevlut Cavusoglu tweeted on Tuesday.

“I’m very clear that there can be no future for Assad in a stable Syria,” British Prime Minister Theresa May said in an interview with the BBC. “I call on all the parties involved to insure that we have a transition away from Assad.”

The civil war in Syria has killed more than 500,000 people in six years and displaced more than half of the prewar population of 22 million from their homes.

Franco Ordoñez contributed to this report.

Vera Bergengruen: 202-383-6036, @verambergen