By Cass R. Sunstein • Bloomberg

Many Americans have forgotten, or never learned about, the Alger Hiss case. One of the most dramatic trials of the 20th century, it helps explain not only the rise of McCarthyism in the early 1950s and the presidencies of Richard Nixon and Ronald Reagan, but also the contemporary roles of Rush Limbaugh, Ted Cruz and the Tea Party.

The Hiss case casts light on why conservatives and liberals are suspicious of each other, on their different attitudes toward elitism, on their understandings of patriotism — and on the parallel universes in which they seem to live.

In his 1948 testimony before the House Committee on Un-American Activities, Whittaker Chambers, a writer and editor for Time magazine and a former Communist, identified Hiss as a Communist. Hiss adamantly denied the charge. He said he didn't know anyone named Whittaker Chambers. Encountering his accuser in person, Hiss spoke directly to him: "May I say for the record at this point that I would like to invite Mr. Whittaker Chambers to make those same statements out of the presence of this committee without their being privileged for suit for libel?"

Chambers took Hiss's bait. In an interview on national television, Chambers repeated his charges. In response to the libel suit that followed, he produced stolen State Department documents and notes that seemed to establish not merely that Hiss was a Communist, but that he had spied for the Soviet Union. Hiss was convicted of perjury.

The conviction was stunning, for Hiss had been a member of the nation's liberal elite. A graduate of Harvard Law School and a law clerk for the revered Supreme Court Justice Oliver Wendell Holmes, he had held positions of authority in the Agriculture, Justice and State Departments. He was tall, handsome, elegant, gracious, even dashing.

At his 1949 perjury trial, an extraordinary number of liberal icons served as character witnesses for Hiss, including two Supreme Court justices (Stanley Reed and Felix Frankfurter); John W. Davis, who was the Democratic presidential nominee in 1924, and Adlai Stevenson, who was to become the Democratic nominee for the presidency in 1952 and 1956.

By contrast, Chambers was short, plump and badly dressed. He was a college dropout. After abandoning Communism, he became a conservative and a Christian, and he saw the 20th century as a great battle between Communism on one hand and religious devotion on the other.

When Chambers initially made his charges, many people, especially on the left, thought he must have been motivated by some personal grievance against Hiss. Chambers responded: "Mr. Hiss represents the concealed enemy against which we are all fighting and I am fighting. I have testified against him with remorse and pity, but in a moment of history in which the nation now stands, so help me God, I could not do otherwise."

As Chambers detailed his relationship with Hiss and their joint work with the Communist Party in the mid-1930s, the sheer accumulation of personal details threw Hiss's denials into serious doubt. Chambers knew a lot about Hiss's son and wife, his hobbies, his various apartments, his automobiles and more. In explaining his relationship with Chambers (whom he ultimately acknowledged knowing), Hiss spoke with apparent conviction, but he also seemed to offer an odd brew of evasions and concoctions.

The Hiss case split the country. Many liberals thought that Chambers was a liar and perhaps a madman. Chambers explained their reaction in a way that fit with, and helped spur, a widespread view on the right: "The simple fact is that when I took up my little sling and aimed at Communism, I also hit something else. What I hit was the forces of that great socialist revolution, which, in the name of liberalism, spasmodically, incompletely, somewhat formlessly, but always in the same direction, has been inching its ice cap over the nation for two decades."

From the beginning, Hiss contended that Chambers intended "to discredit recent great achievements of this country in which I was privileged to participate," including the New Deal. Among conservatives, Chambers became a hero, and his 1952 autobiography, "Witness" — moving, poetic, an unforgettable mixture of pessimism, spirituality and hope — became an instant classic.

Most of those who have carefully studied the case, and who have explored evidence emerging long after the trial itself, have concluded that Chambers was telling the truth and that Hiss did indeed perjure himself. But the legacy of the case extends well beyond the issue of Hiss's guilt.

Chambers' broader charge — that liberalism was a species of socialism, "inching its ice cap over the nation" — polarized the nation. His attack on the patriotism of the Ivy League elite reflected an important strand in American culture, and it helped to initiate suspicions that persist to this day.

Liberals are no longer much interested in Hiss's conviction. Yet they are puzzled, and rightly object, when they are accused of holding positions that they abhor. We can't easily understand those accusations, contemporary conservative thought or the influence of the Tea Party without appreciating the enduring impact of the Hiss case.

Cass R. Sunstein, the Robert Walmsley University professor at Harvard Law School, is the former administrator of the White House Office of Information and Regulatory Affairs, the coauthor of "Nudge" and author of "Simpler: The Future of Government."