How do you think Clinton would respond to chemical weapon use, if she were president now? Especially a second use as in this case? If this does turn out to be a one-night strike against a relatively small number of targets, it's smaller than what I would expect her response to be - a sustained campaign of strikes not unlike the Libyan intervention, although smaller in scale and intended duration. Any sustained campaign would be much harder for Putin not to respond to.
Not that Trump isn't a dangerous warmonger as well, of course. This could very easily spiral out of control, especially if he starts seeing this as a reliable way to direct coverage away from his scandals, or if Bolton gets him to launch more attacks in the future.