The next president should not be in his seventies . . . or his eighties.

I realize that is age-ist, but the presidency is one of the hardest jobs in the world, and executing the duties of the presidency well requires someone who is in good physical and mental health, ideally with a lot of vigor and an ability to handle off-the-charts stress and a relentless workload.

Joe Biden was not the most verbally or mentally disciplined guy back when he was vice president, and his advancing age is worsening his problems. The president really can’t speak off-script anymore without blurting out something that undermines the case he was trying to make. Republicans may not mind having a president who is so ineffective, but over the long term, it isn’t good for the country to have a commander in chief who can’t handle portions of the job.

A good recent example came on Monday when Biden was discussing gun control, and left the impression that he wants to ban nine-millimeter rounds, the single most popular handgun round in the U.S…