The American President, as an extra-constitutional power, can define the New Hitler. The New Hitler is foreign, stubborn and resistant to Our beneficial designs. Resisting Our Will. It is not a war crime to bomb a passenger train, blow up a television station, starve half a million children, flatten an aspirin factory, aid and abet drug dealers, decimate refugee convoys, arm terrorist organisations and then lie about it all. Because we pay the cost of the tribunals.
Isolationists are vicious, backward looking and popular.
Isolationists oppose war, because they want war. Isolationists are racist because they oppose killing foreigners. Because they do not want their own country in needless foreign wars. Hitler went on aggressively expansionist wars in the process bringing his country's moral standing and economy to unbelievable depths. So the isolationists must be for that.