This would NOT be the first U.S. President suffering mental Decline

In fact, it is a well known fact that Nancy Reagan was our de facto President during Ronald Reagan's last 2nd term because he had serious Alzheimers by then and she "covered" for him and told him what to do and say so he appeared relatively normal. And because he was a good actor in movies he could pull this off.

Also, Andrew Johnson after Lincoln was assassinated was pro--slavery who supported the "Carpetbaggers" who harmed everyone in the south to take advantage and almost created a situation where slavery was once again re-instituted in the South. So, like Trump Andrew Johnson was a white racist who was Lincoln's Vice President who became president after Lincoln's assassination. Because of this the people of the U.S. fought back by putting in General Grant who was considered a hero of the Civil war and  who allowed slavery to die finally in the South while he was president. They put in General Grant as U.S. President from 1869 to 1877 which ended slavery for good in the South.

So,  having a president with obvious mental decline, Trump isn't the first president to have this problem because Reagan had this problem first and likely others also before him. The problem with Trump is that Trump is obstinate like many older men and won't let anyone advise him. That's why Trump is such a danger to our democracy much like Andrew Johnson was before him. This is why Trump needs to be impeached or to have more democrats put into office to prevent his further harm to our democracy soon.

If you actually listen to what Trump says even in his tweets he contradicts himself multiple times if you are a clear, rational and logical thinker. So, if you can think clearly and logically you see him fight himself and what he says sometimes in the same paragraph so all logic and reason is lost in the conversation of whatever he is saying.

Now, one could make the argument that Trump is so used to lying and misdirecting in his speeches that this is what is happening but sometimes it's as obvious as "Putin didn't interfere with the election but I agree with our intelligence agencies that Russia interfered with the elections and still is."

You cannot be saying both things in the same paragraph unless you want people to think you are a fool at best or have Alzheimers at worst or senile dementia.