Joe Biden’s cognitive deficits are increasingly apparent, even to the most amateur observer. Whether or not he has dementia at this point is immaterial. Half the world thinks he does and that weakens the United States and imperils us all. Whether he is falling up the stairs of Air Force One or falling off a stationary bike, whether he is wandering around on stage in a fog or clutching cheat sheets designed for a 4-year-old, whether he is shouting incoherently or whispering creepily, the optics are shocking. With his 80th birthday approaching next month, even if most Americans are too...