It's more than that, it's unbelievably dangerous. There's a reason world leaders don't do stuff like that in public, we just signaled loud and clear we're absolutely not to be trusted. If China wants to make a move on Taiwan, the DPRK wants to shell Seoul, or Russia wants to test Article 5 they just got a lot more confident in our lack of conviction. And all our allies had better be drawing up contingencies that don't involve us coming to their aid.