It has been a bad week for presidential sibling loyalty. Juanita, sister of Cuba’s Fidel and Raoul Castro, revealed she was on the payroll of the CIA in the 1960s, while Ahmed Wali, brother of Hamid Karzai of Afghanistan, stood accused of being a more recent recruit, although he denies it.

The intelligence agency would have needed to look no further than home, where it is not supposed to operate, to come up with the idea. None of America’s 44 presidents has been an only child; and many siblings have proved thorns in the flesh.