the communist movement was gutted under McCarthyism

The communist organization was gutted under J. Edgar Hoover. McCarthy just picked off the stragglers.

For better or worse, it was WW2 itself that split the American Communists, as they wrestled with the old Leninist urge towards anti-war activism as a proletarian rallying cry and the Stalinist plea for interventionism on the Western Front. The internal reaction to the assassination of Trotsky, the protests against FDR at the peak of his popularity, the championing of civil rights movements back when segregation was fully normalized, the turmoil produced by various intraparty sex scandals, the repeated violations of the Smith Act that the FBI pounced on, the CIO's throwing the party under the bus to appease Truman, the nuclear espionage... it all fouled the party's national image and the economic philosophy as a whole.

By the Cold War, US Communism was a shadow of its former self and Global Communism was fully in the thrall of sectarianism (absent the odd Third Worlder like Tito). But that was all largely due to the success of the Russian Communist experiment (and the Chinese experiment, hot on its heels). There was never a comparable movement in the west, in no small part because US industry was too successful at appeasing the American public with consumer surpluses even at the height of WW2 rationing.

Communism, as a socio-economic philosophy, has a very hard time taking root in the imperial core precisely because it is so bound up with anti-imperial economics and self-sufficient policies. Sakai was right on that much, at least. You can't sell an American or a Brit or Frenchman on self-determination when imperial extraction is so much more lucrative. The Settler isn't going to buy an economic plan that strictly benefits the native laborer by internalizing their surplus.

At absolute best, you could see American Native People and segregated workers take up the banner. But as soon as capitalism becomes color blind, the Black Socialist losses footing.

FDR saved capitalism from itself with social democracy. He was the one responsible for killing communism in its craddle. Had Hoover and Dewey been allowed to do libertarian white nationalist capitalism for another twenty years, you might have seen American communism take firmer root. But FDR, Truman, LBJ, Carter, Clinton, and Obama have been far too good at expanding the economic borders and perpetuating the illusion of upward mobility.