He called the attack that almost destroyed Shayrat military base near Homs, in the country's west, "a pity", suggesting the US President had been pressured into the act by the Pentagon.
"Russian cruise missiles strike the terrorists, US missiles strike Syrian government forces who are spearheading the fight against the terrorists," he added.
A US defence official said Russians were present at the base, and the US military contacted its Russian counterparts about the attack ahead of time. But this does not appear to have been enough to prevent the icing over of relations.
Trump's core supporters in the US also turned on him over his change of attitude towards Syria, with right-wing commentators declaring themselves "OFF the Trump train".
US pundits hazarded that President Bashar al-Assad "must be stunned" at the huge missile strike.
The Syrian regime has been "carrying out mass atrocities against Syrian civilians at will" for years, wrote Dexter Filkins in the New Yorker, and only now has a punishment been meted out.
Trump's former fiercest detractors took the extraordinary step of praising the US President.
An editorial in the New York Times, habitually engaged in a war of words with the unpredictable commander-in-chief,said Mr Trump was "right to strike" and "should be commended".
The Wall Street Journal said the President had "demonstrated a comfort with military action and a flexibility in approach that saw him change course" on Syria just 48 hours after horrific images of the 80 civilians killed in chemical attacks emerged.