Donald Trump's recent conduct and stance on Greenland have many experts thinking that the time has come for the 25th Amendment to be used against him, as the President seems to be displaying behavior that makes him incompetent to be a good leader.
This includes a very bizarre diplomatic letter shared with a foreign leader that clearly shows how he's no longer fit to carry out the duties of his office.
Trump sent Norway's PM a weird message where he expressed serious anger over not getting the Nobel Peace Prize and coupled this grievance with talks about possibly seizing a distant territory that is under the leadership of Denmark.
What should have been legitimate diplomatic communication turned out to be erratic behavior and was driven more by personal ego instead of sober leadership.

Many called his stance irrational, and his claims exaggerated when it came down to foreign policy, threatening alliances, and focused more on obsessively personal accolades.
This behavior demonstrates clearly the dangers to global stability and suggests that the president might be facing issues with his mental and physical fitness. This is why experts feel invoking the 25th Amendment is the best possible solution in this situation.