Jon Wiener teaches US history at UC Irvine. Excerpted from his new book “How We Forgot the Cold War: A Historical Journey Across America.” 

The most popular National Park Service site is the Blue Ridge Parkway in Virginia, which has around 17 million visitors per year; the least popular seems to be the Whittaker Chambers pumpkin patch National Historic Landmark near Baltimore, which has around two visitors per year. I was one of them. One windy fall day, I set out from Baltimore with friends to search for the pumpkin patch. The Reagan administration designated it a National Historic Landmark (officially called “Whittaker Chambers Farm”) in 1988 over the unanimous objection of the National Park Service Advisory Board. The site, outside Westminster, Md., commemorates the spot where, in 1947, Whittaker Chambers reached into a hollowed-out pumpkin and pulled out some 35mm film. He said it showed that Alger Hiss, a pillar of the New Deal, had been a Soviet spy.

The “pumpkin papers” helped convict Hiss of perjury in 1950, which transformed public opinion, convincing Americans for the first time that communism posed a real danger to the country. The obscure congressman named Nixon who pushed the Hiss case won a Senate seat the year Hiss was convicted and got the vice-presidential nomination in 1952; a month after Hiss’s conviction, Sen. Joseph McCarthy gave the speech in Wheeling, W.Va., that launched his career and gave the new, virulent anticommunism its name. For the next 45 years, the Cold War served as the iron cage of American politics.

Conservatives had hoped this site would provide a place where the public could be told that the Communist Party did not just defend a totalitarian regime but also recruited its members to spy on that regime’s behalf. Thus the hunt for communist spies was not “McCarthyism”; it was a noble cause....