Circulating on social media is speculation that sometime last October or November Trump suffered a stroke.
Posted as evidence to support this are statements that he has trouble lifting his right hand above his waistline, is dragging his right leg, the right side of his face is drooping in his ‘official’ photo, and noting in pictures what seems to be a very bruised back of his hand, indicating that he had an IV inserted at some point.

Add to that the inability to pronounce simple words at this rally video below, and it is not hard to imagine that this theory could be true.

Of course the Trump camp put out an out-and-out denial that any such thing happened.