There are a lot of erroneous assumptions that need to be disentangled here.

Firstly, there was a significant anti-communist movement within the interwar United States. The First Red Scare of 1919-20 saw a heightened federal and state hounding out of suspected communist and anarchist sympathizers within the US. United States Attorney General A. Mitchell Palmer used a variety of legal and semi-legal methods to break the back of alleged communist organizations and networks. Palmer's shrill rhetoric managed to go too overboard and led to the abatement of the First Red Scare, but there still remained very strong networks of anticommunism in American business and government. The Hearst newspapers struck a very consistent anticommunist drum throughout the 1920s and 30s and a number of Hearst columnists decried "red" influence in Hollywood and the New Deal. Republican and other opponents of the New Deal also lambasted it as communist-inspired program. Father Coughlin, for example, trafficked in a fusion of antisemitism and anticommunism to attack the Roosevelt administration- see this clip of his disgusting speeches which he threads this needle. One of the elements of J. Edgar Hoover's building-up of the FBI into a major federal institution was to incorporate a dogmatic anticommunism within its ranks and investigate communist groups. The House Un-American Activities Committee (HUAC) actually began its life in 1938 and was tasked with rooting out a broad variety of domestic threats to the US, communist parties included.

The US's diplomacy with the USSR was also far from warm in the interwar period. The legacy of America's intervention in the Russian Civil War in favor of the Whites did cast a long shadow over US-Soviet relations with the US only establishing formal diplomatic relations with the USSR in 1933. There were trade deals and other initiatives before 1933, Henry Ford famously opened up an automobile plant in the USSR, but these were on the whole rather minor affairs. The Roosevelt administration, like the UK, tended to be skeptical of Stalin and his motivations. Diplomatic relations throughout the 1930s between the US and the USSR were often rather frosty.

Domestically, the CPUSA at times sided with the New Deal and the Democratic Party, but the White House did not actively court the CPUSA as an ally. For its part, the CPUSA largely adapted to the Popular Front tactics of Western Europe and deemphasized some of its more radical elements of its platform like violent proletarian revolution. The CPUSA thus managed to gain some access into working class unions and among intellectual circles that had hitherto been resistant to communist penetration. The more flexible politics of the Popular Front period, the clear ideological enemy in the form of fascism, and the spectre of the Great Depression all made communism an attractive political ideology for some Americans. But an open championship of communism never became part of the American political mainstream, even in FDR's New Deal.

While it was clear that the Roosevelt administration was much more hostile in the interwar period to the Third Reich than to the USSR, but this was because Hitler provided much more of a clear threat. Hitler's economic policies of extreme autarky and rearmament put an even greater squeeze on US-German trade. German exports to the US fell from ca. 1 billion RM in 1929 to 150 million RM in 1938. American exports to Germany likewise fell from their high of 2 billion RM in 1927 to hovering at under 300 million RM for most of the thirties.American boycotts certainly ate into German imports and caused increased tensions between trading partners. The free-trade impulses of the Roosevelt administration also ran afoul of the Third Reich's protectionism. In 1934, Berlin unilaterally abrogated its trade agreement with the US, hoping to renegotiate a treaty allegedly more equitable to Germany by granting German firms special concessions in the US market (ie a trade agreement that benefited Germany). Such an agreement was a dead letter both for the Roosevelt administration and much of Wall Street despite fears of being cut off from the German market. A year before pulling out of its trade agreement, Berlin also suspended payments on its debts, further making it harder for the US to come to terms with Hitler. These economic rows also came on top of Hitler's own aggressive foreign policy in which he stoked the Spanish Civil War and began to occupy portions of Eastern Europe. In short, Germany was acting like an archetypal rogue state which was bound by no conventions and could not be dealt with on an honest level.

In contrast, the main dictatorial excesses of Stalin in the 1930s were domestic in nature. Stalin's moves in Eastern Europe only began after the war broke out in 1939. Collectivization and the Purges did manage to kill a multitude of Soviet citizens, but they were not fundamentally disruptive to the international order. The Stalin turn also strengthened what already was a very closed system in which foreigners had very little access. The famines that came with collectivization thus tended to be undereported in the West. Popular stereotypes of Russian moroseness also played a role in downplaying reports of the Soviet dictatorship as a number of intellectuals assumed that Russians have a tendency towards pessimism and alienation just like the characters in Tolstoy or Dostoevsky. In contrast, German policies against Jews and other dissident groups took place rather openly and in full view of the Western press. German propaganda also deliberately and openly pushed for Weltmacht and Hitler's diplomatic actions justly gave this propaganda a degree of validity. Stalin's diplomatic moves always remained much more mysterious and harder to pin down for outside observers.

Nonetheless, while the hostility to the Third Reich was far greater than the USSR in the interwar US, the American political establishment was not exactly on warm terms with communism. Many of the institutions and people involved in the shrill anticommunism of the postwar Second Red Scare cut their teeth on anticommunism in the 1930s. Hearst columnists like George Sokolsky were already inveighing against American communists subverting America in the 1930s and even during the war. These media figures further developed the idea that the US was soft on the Soviets and communism under FDR, when the truth was much more complicated. Congressmen like Martin Dies had already shown the political value of anticommunism, a lesson a junior Senator from Wisconsin, Joseph McCarthy, would use to resuscitate his flagging career. The Second Red Scare did not come from nowhere and its roots stretched back into the 1930s and 20s.

Sources

Berghahn, Volker R. American Big Business in Britain and Germany A Comparative History of Two "Special Relationships" in Twentieth Century. Princeton: Princeton University Press, 2016.

Ceplair, Larry. Anti-Communism in Twentieth-Century America A Critical History. Santa Barbara, Calif: Praeger, 2011.

Storrs, Landon. The Second Red Scare and the Unmaking of the New Deal Left. Princeton: Princeton University Press, 2013.