Jack was no ally. But it’s safe to say Jack wouldn’t have had a career without Joe McCarthy.
The bottom line is that no one who seeks power should be trusted. Ever. That’s not to say that all who seek power are bad, and that all who have a desire to work in the public sector are dishonest or Machiavellian. Nonetheless, they still should not be trusted. The stakes are too high, and human nature is human nature.
More to the point, Joe’s indifference to the threat from Hitler was owing to his fear of The Soviets. Germany came close to a Red take-over in 1919-20 and Nazism, like Italian Fascism, was a counter-stroke. Of course, In totalitarian states, everything turned on the character of the men at the top, and Hitler, like Lenin, Mussolini, and Stalin cared about nothing except power. Looking back, I wonder how much Joe Kennedy suspected about Hopkins and Red Influence in the White House?