Communism was disturbingly trendy among American intellectuals during the '30s, but I don't think it ever had the mass support necessary to take power. The Bolsheviks had a St Petersburg Soviet in 1905 as a dress rehearsal for 1917 and the CCP governed base areas like Jiangxi well before it took power in 1949. America had a bloody labor movement before WW1, but American socialist revolutionaries never controlled a territory like their Chinese and Russian counterparts did.
Fascism might be even harder to get in the United States. Fascism took power in Italy, Germany, and Austria where democracy was unconsolidated or the transition to universal suffrage was relatively recent. The conservative aristocratic establishments weren't on board with this newfangled democracy thing, and the labor movements hadn't accepted a nonviolent, parliamentary role they played in postwar social democracy.
Fascists also relied on powerful revanchist sentiment and a desire for living space that would fall on deaf ears in the US. America bought most of its "living space" from France, conquered it from Mexico in the 1840s and had settled it all well before the 1920s. Anyone who wanted the prestige of a colonial empire had the Philippines, Puerto Rico, Hawaii, Alaska, the canal zone, and the Caribbean subject to varying degrees of de-facto US protectorate.
I don't think ideological antisemitism would be popular in the US the way it was in Europe. The Confederate States, the most reactionary state in US history, allowed a Jewish politician to serve as its Secretary of State and Secretary of War. American history has its shameful episodes like Leo Frank's lynching and Henry Ford's loony publications, but the US is generally better than the old world on this issue. The US has never had a state religion or required elected officials to be a certain denomination, there wasn't an American Jewish struggle for legal emancipation like there was in Europe.
The American nativists had largely gotten what they wanted on immigration with the restrictions passed in 1924. American reactionaries' focus would likely be delaying civil rights as long as possible (basically OTL) and maybe keeping prohibition around longer. Organized crime would keep milking the cash-cow of bootlegging. and civil rights would happen embarrassingly late ('70s or '80s), likely with more civil unrest involved. This would be a nastier, less enlightened version of OTL, but it wouldn't be a totalitarian break with the past like Stalinism and National Socialism were.