The thing is, a lot of the isolationists at the time were more worried about Stalin, than Hitler.
The Non-Aggression Pact should have sent shivers through their spines, because the big fear was that Stalin would be the big winner in the end. That fact alone probably converted a lot of the isolationists.
The Times picked up on that rather perceptively. The fear was that Stalin was counting on a prolonged Anglo-French/German war that would eventually exhaust both sides. Then he could clean up by advancing his “proletarian revolution” into Western Europe. That was in fact exactly Stalin’s calculation. Add to it that Stalin needed time to rebuild his army after shooting most of his officers while simultaneously expanding it from a standing force of 1.5 million men to about 5 million men. Stalin needed the breathing space as much as Hitler needed him out of the picture. Not too many in the West realized this at the time, but it will become apparent when the Soviets try their hand with tiny Finland in a few months.
Stalin miscalculated; Germany beat the French quickly and he got far less time than what he’d thought he’d have.