He could be convinced to resign, but that’s so far outside the realm of plausibility as to be dismissed without further consideration.
There’s also removal for unfitness by the Cabinet, but that’s also entirely implausible for various reasons. (Edit to add: I just did a search, and there doesn’t seem to be a dedicated single thread on this subject to which I can quickly refer you. It’s come up many times in other threads, been discussed briefly, and then dismissed. Here is one example. You can search for “25th amendment” to find other similar references.)
But that’s it, in terms of legal paths.
There is another option but we are forbidden from discussing it.