Donald Trump has demonstrated his lack of fitness for the presidency in countless ways, but one of the clearest is in the company he keeps, surrounding himself with fringe figures, conspiracy theorists and sycophants who put fealty to him above all else. This week, a series of cabinet nominations by Mr. Trump showed the potential dangers posed by his reliance on his inner circle in the starkest way possible. For three of the nation’s highest-ranking and most vital positions, Mr. Trump...