Trump also has said "I will bomb the shit out of them -- I don't care" on the campaign trail.

I think a relatively accurate model of the people's opinion towards intervention might be quite simple: it is good if we win relatively swiftly and bad if we lose and/or don't gain anything, and the opinion at the time is shaped (and over time altered) based on their estimate of the outcome, but no politician says it that way so it is always cast as black and white pro-war/anti-war.

In the current case, I think many Americans, even Democrats, recognize the regime in Iran as a threat that needs to be dealt with somehow (a deal or an intervention). Their worry is the cost and ramifications, not some ulterior principle. If Trump brings home a win and some oil to boot soon-ish, you're going to see positive sentiments more clearly. If this drags on, the backlash will be there, and will be phrased as "MAGA never wanted the war" and along your lines of isolationist promises not kept.