I think it is premature to assume that this presages a larger scale engagement with Assad's regime, or with Russia. There is little I would put past Trump, but I don't necessarily think we can assume it at this point. Also, as was pointed out on page 1, Trump probably didn't personally make the call to shoot down this plane.
There are things here which need to be investigated, regardless of what the investigation ultimately turns up. If Trump does terrible things in order to deflect from a necessary investigation, that is on him, not the people who are investigating, and not the people who support the investigation. I don't understand how Trump's bad foreign policy is anyone else's fault but his own.