I totally agree that motives are internal and unobservable.  But in the case of Trump, for example, his enemies frequently attribute malevolent motives.  If we agree not to discuss personal motives, it would be an improvement.  But now in regard to "Assad," he is not the issue really, it is the entire Syrian government.  That institution may reasonably be ascribed the desire to maintain power - otherwise they would have capitulated to the killer rebels long ago.  The use of chemical weapons which predictably inflame the west is not in the best interests of maintaining power.  Chemical weapons are not magic.  If they could have significantly improved military success, then the Syrian government might have been tempted to use them despite anticipated negative fallout internationally.  The airstrike could have achieved all objectives with conventional HE bombs.  So why use chemical weapons?  Insanity?