The map would look very much like a map from 1953 of people who believed that Julius and Ethel Rosenberg were innocent of spying. (Ethel possibly was innocent but was willing to die with her husband.) Most of those people still believed that communism was a reasonable ideology and that the charges against Stalin were exaggerated. They also believed that charges of Soviet spying were fictitious. (Over 200 people in high ranking government jobs were actually spies, but the evidence was from deciphered codes that couldn't be used in court ... most of the 200 were confronted and pressured to resign.)
My point is that communism (with a small C) was a lefty value system that had several million Americans hewing to a “party line.” The party line replaced theism. Today the heirs to this system of thought still hew to a party line. I get the party line in every gathering of San Franciscans. Some people get the party line from Doonesbury, others from friends who read Doonesbury. The rest just figured out that being opposed to everything George W. Bush proposes is the simple way to follow the party line.
Of course there are exceptions to the “no religious affiliation” such as liberation theology Catholics and a few National Council of Churches Protestants.