There is ample film footage of him shuffling on and off aircraft.  It is easy enough to make your own assessment of his overall mobility.

It used to be said that Al Gore was only one Big Mac away from the presidency.

Well, consider President Obama playing hoops.  Five minutes of that for Donald Trump and they would be swearing in Mike Pence before night-fall.

The instant Donald Trump ceases to be useful to the oil industry, the next morning they will find grounds to impeach him.  Politics is a dirty business.  He has a closet full of skeletons, and he has publicly rebuked they entire leadership of every intelligence organisation of the US government, including the FBI.

That is a recipe for impeachment faster than you can spell "J Edgar Hoover".