After decades long alliannce-building, the US don’t seem to value them anymore. It’s a strange phenomenon where someone works so hard for such a long time, only to throw it all away some day. Trump frames it all as if the US is being taken advantage of. The truth is that the US gets tremendous benefits from it’s central position of power. If the US breaks away from their alliances, they risk the tides turning against them. If the US is being taken advantage of by appararently all others countries in the world, isn’t it remarkable how it’s doing so well economically? That normal folks aren’t doing well is not a consequence of the economy as a whole not doing well, because by comparison it’s doing phenomenal. It’s because all the money goes to companies and shareholders.
I don’t see why this is ‘almost certain’. You rightfully point out that the EU clause leaves wiggle room, but I don’t see why you think that room is not there with NATO. I don’t know if the current US president cares much about any precedents. If he can wiggle he will wiggle. I don’t think Europe trusts US to honor A5 any more.