And losing control of Congress after 14 years due to Red Scare tactics being leveled against Democrats who didn't in the least deserve it (does Jerry Voorhis look like a Communist?) was just a minor inconvenience, I guess.
Although the Red Scare itself didn’t get underway until 47, Truman and the Dems had already turned on labor by the 46 elections. Their pro-management response to the 45-46 strikes alienated the unions, who as a result weren’t too inclined to help Democratic candidates. That and Truman’s poor handling of the postwar price situation were the main drivers of the GOP wave of 46. The GOP wasn’t able to effectively use the “soft on Communism” line against Dems until China fell.