Equally ridiculous quip from that link:
Well, that's mighty big of him. See levels rising? Well, we're certainly not going to do anything about it at a national level, but if you want to rebuild your roads, have at it!If cities like Miami Beach want to set local rules to fight the effects of rising seas, though, Trump said he wouldn’t get in their way.
“If the local government feels that way, they should do it,” he said. “If they’re doing the roads, and if they want to make them higher, I think that’s probably not the worst thing I’ve ever heard, if you’re going to do them anyway.”
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I think the most parsimonious explanation is that he's a blowhard dipshit. All of his behavior is consistent with this hypothesis. He says a bunch of stupid shit, gets called on it, figures out that maybe it's wrong, and then says, "what do you want, I was joking you dummies!". I've known a couple people like this.