Okay, let's get to the nature of what you would accept as evidence. What if the Washington Post wrote an article whose author said he had talked to an unnamed foreign policy expert who said that during a foreign policy consultancy session, Trump asked him why the US can't use nuclear weapons three times. Would you accept that as evidence? Not in a court to put anyone in jail, I mean as evidence that it happened personally?
You're barking up the wrong tree. You can build a time machine; hand walk Trump supporters into the security meeting while it's happening; physically restrain the Trump supporter so he's less than 3 inches from Trump's mouth while he asks the question 3 times... and this is how that idiot will respond:
1. I didn't hear him ask those questions;
2. Okay, he asked those questions but he was being sarcastic;
When the asshole Trump supporter leaves your space, he'll respond by saying something along the lines of...
3. Trump's right. We should be able to use nuclear weapons anytime, any place, for any slight. China's balking at the Trump trade deal? Nuke em. Mexico doesn't want to pay for the wall? Nuke em. Jimmy Kimmel or another late night host makes fun of his hair? Nuke the city where the show is produced. (And of course the last three sentences are facetious in nature ... have to write that out because Trump supporters are a tad brain damaged ... at best).