Out of serious things, war against Iran in 2019. I mean he was escalating in it first place and probably kicking and screaming when Pentagon people explained it's not a good idea when Iranian air defense shot their 200million stealth drone with 60's Soviet missile, but he did. He also ordered Soleimani murder to have the last word later. Also Bolton accused him of being way less hawkish and having more common sense than average Rep senator, but that says more about Rep senators than Trump.