George Norris, senator from Nebraska between 1913 and 1943.
Norris was a champion of progressive causes of all stripes. Although a Republican for most of his career (in 1936 he left that party and became an independent), he fought hard on the side of working people. He strongly believed that an activist government could solve many of the nation's intractable problems. He was largely responsible for the Norris-LaGuardia Act in 1932, outlawing yellow-dog contracts (agreeing to not join a union as a condition of employment). But Norris' great passion was public power. He was the single most passionate architect of Tennessee Valley Authority style programs to lift entire regions out of poverty. In fact, he once helped nix a Henry Ford program to build dams in the Tennesee Valley because he knew it was government's place, not private investors', to develop the country. When Franklin Roosevelt took the presidency, Norris' dreams were realized. The creation of TVA in 1933 owes a great deal to Norris' vision. Among the first dams built was Norris Dam, named after the great senator. Fittingly, TVA also created an experimental planned community near the dam for its workers and other locals, providing decent housing, tree-lined streets, schools, and other amenities virtually unknown in the deeply impoverished Tennesee Valley.
Actually, I am a huge critic of TVA and other high modernist dam projects. They have proven environmental disasters of the highest orders. They rarely provided the benefits promised to people and they often ran roughshod over local opposition. However, such ideas were completely unknown to political and intellectual communities in the 1930s. Dams seemed like a savior and political division over them revolved around whether they should be public or private. Norris and New Dealers at large believed public power would raise the standard of living for millions of Americans. Even if they were arguably wrong on the role of dams, they certainly were correct about activist government in general.
On a related note, Sandy Levinson examines the whole idea of great senators and pretty much agrees with me (or I with the much more famous Levinson) on what constitutes a "great" senator. He criticizes Robert Caro, Lyndon Johnson's biographer, for romanticizing so-called "great" senators irregardless of their actual beliefs and the effect of their actions.
So that brings us to Calhoun, a thoroughly brilliant man who devoted his considerable talents, for most of his career, to nurturing and defending chattel slavery. It's really as simple as that. The United States would have been better off had Calhoun been thrown from a horse and killed in, say, 1827. Caro, whose books on Johnson and both great and flawed by a tendency to demonize at times a remarkably complex man, has an untenably romantic view of "great senators."
It is, indeed, like those say that both Churchill and Hitler were "great leaders" because, along some totally amoral metric, they were able to move their audiences to do remarkable things. Well, yes, but anyone who stops there is a moral idiot.
Precisely. That's why John C. Calhoun deserves our scorn as a moral scoundrel and a horrible man who did more than any single other person to justify and glorify slavery as a "positive good." Any discussion of Calhoun as a great senator comes from a person who doesn't believe morality matters in politics.