Which president said swap horses in the middle of stream?

The saying "don't change horses in midstream" is often attributed to President Franklin D. Roosevelt (FDR), though there's no evidence he ever actually said it.

It was a popular saying during his presidency, used to justify his decision to run for a third term in 1940 during World War II. The idea was that it was dangerous and unwise to change leadership in the middle of a crisis.

While FDR didn't invent the saying, he was certainly associated with it. It became a popular political slogan used to discourage switching political parties or presidents during difficult times.