Finally - much too late - the Syrian government allowed the UN inspectors to have a look at the alleged chemical attack sites. Immediately we saw Washington react with the message that it was too late. At the same time Obama adopted a more hostile tone.
This is a familiar pattern. It shows that Obama doesn't care about what Assad is doing and is only obsessed with getting his "regime change". From that attitude the forthcoming reaction of Assad was unwelcome and had to be compensated with more hostility from the US side.
If Obama had been interested in dialogue and solutions he would have welcomed the Syrian change of policy. Not that it is such a great gesture or that it will make much difference. But simply because any improvement in attitude should be rewarded if you want to have better relations.
It is not improbable that Obama has already decided to some retaliatory attack. But even in that circumstance it is still the case that communication should not be unnecessarily hampered.