The 25th amendment does provide for the removal of a president who is deemed "unable to discharge the powers and duties of his office." But it's a mechanism that relies on the judgment of the VP and a majority of Cabinet members, plus confirmation by Congress. Unfortunately, the opinions of mental health professionals aren't relevant except insofar as they compel government officials to take action.

So, as always, it comes down to politics. Does the VP have the will to start the ball rolling and, if so, will the Cabinet and Congress back him? You don't start something like this unless you're absolutely sure you can succeed. The last thing we need is an angry, vengeful Trump left in office feeling isolated from both his party and his administration. That could be catastrophic.