Secretary of State Rex Tillerson said just last week that the United States was no longer pursuing a policy of regime change in Syria and that Mr. al-Assad’s fate would be “decided by the Syrian people.”.....

Then came the unexpected, and strategically unnecessary, chemical-weapons attack on Khan Sheikhoun, which was followed by the rapid spread of video evidence showing children and what Mr. Trump called “beautiful babies” gasping their last breaths after being exposed to sarin gas.
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Judging from the past pattern, it should be "well expected".