Well its the usual crew taking the moral high ground, or using the excuse of a moral high ground to do something they have been wanting to do for a long time. Public opinion is an important fulcrum in this, after Russian involvement in conspiracies against western democracy, the use of chemical agents and supporting Syria who according to international agencies has used chemical weapons against civilian populations, public opinion is certainly against Assad and Russia, whether its pro involvement is another question entirely. Also its not only Trump, as he actually promised less involvement in foreign conflicts, but with the UK and France, who are also two nuclear powers, to back up US involvement, we'll see soon how this escalates. Syria has always been a proxy and I don't think there are any official Russian troops still on the ground otherwise the US wouldn't have acted. Still it's bat shit crazy.