I urge you to look at the facts. Both instances of Assad using chemical weapons against his people were preceded by Trump, or others in the administration, making statements that suggested they would not care. In this most recent case, it was Trump saying he wanted to end American involvement in Syria.
Sure, Assad miscalculated. But we gave him that chance because of this bumbling administration is incapable of speaking consistently on foreign policy. You want another example of that? How Haley speaking over the weekend to the UN and promising that on Monday the United States would be announcing new sanctions on Russia. Then Monday roles around and it turns out the President has thrown her under the bus and decided to not impose the sanctions.