... In some ways, Sanders’s career calls to mind the four-term Oregon Senator Wayne Lyman Morse, whose fierce opinions and commitment to something he called “constitutional liberalism” annoyed both major parties. Morse, like Sanders, never let party labels fence him in. He won his first Senate term—his first public office—in 1944, as a Republican, and then, in the early fifties, was quick to condemn the demagogic excesses of a fellow-Republican, Senator Joseph McCarthy. He supported President Harry Truman on civil rights while pointing out Truman’s past with the corrupt Pendergast machine, of Kansas City, and left the G.O.P. after the election of Dwight D. Eisenhower, in 1952; among other things, he didn’t like Ike’s choice of the California senator Richard Nixon as a running mate. He then became an independent (not having an assigned seat, he once took a folding chair to the Senate floor), and, three years later, switched parties again, calling himself a Democrat. In August, 1964, Morse was one of only two senators, along with Alaska’s Ernest Gruening, to vote against the Gulf of Tonkin resolution—a “pre-dated declaration of war,” Morse said—which gave Lyndon Johnson, the Democratic President, carte blanche to widen the Vietnam War, much as the Iraq-war resolution of October, 2002 (opposed by Sanders, then a congressman, and favored by Clinton, then a senator), made it easier for President George W. Bush to launch the disastrous conflict in the Mideast.

Morse, who was reared in Wisconsin, was a perpetual dissenter, influenced by the progressive, populist Wisconsin senator Robert La Follette. Like Sanders, he worried about American overreach in foreign policy, and, like Sanders, he was a lonely legislator. Independents usually are—even those who switch in order to survive, like Connecticut’s Joe Lieberman, who became an independent Democrat in 2006, after losing his Senate reëlection bid in a Democratic primary. Morse, in 1960, also ran for President as a Democrat, though not with Sanders’s success, no doubt because of the robust competition he faced. He quit the race after he lost the Oregon primary to John F. Kennedy, the Massachusetts senator and eventual nominee. He lost his Senate seat, in 1968, to a liberal Republican, Robert Packwood; when he died, six years later, at the age of seventy-three, he was attempting to win it back. ...