Howells’s socialism originated in an ethical crisis. He attended court to watch trials; he visited factories. He defended those accused of the Haymarket bombing. Liberalism failed him. He could no longer believe, as he once did, that in the United States the ills that afflicted humanity could “be averted by honest work and unselfish behavior.” By the late 1880s what he had called the “smiling aspects” of American life seemed to be disappearing.

Howells regarded socialism as “not a positive but a comparative thing … Every citizen of a civilized State is a socialist.” If anyone believed “that the postal department, the public schools, the mental hospitals, the almshouse are good things; and that when a railroad management has muddled away in hopeless ruin the money of all who trusted it, a Railroad Receiver is a good thing,” then that person embraced socialism. Howells believed that “the postal savings-banks, as they have them in England; and national life-insurance as they have them in Germany are good things.”

Like Howells, Bernie Sanders embraces a series of modest changes. Mr. Sanders often rightly seems bewildered that free public college education — once the norm in California — and the universal health care of Canada and Europe can seem to be radical solutions to American problems.

Opponents of socialism cast such proposals as dangerous and un-American, but Henry James was closer to the truth when he described the limits of Howells’s imagination. He thought Howells’s deficiencies as a novelist arose from his being too much at home with “the moderate, the optimistic, the domestic, and the democratic” to take great risks. James could have been describing Howells’s socialism and that of his contemporaries. Frances Willard, for example, was an evangelical Christian and a self-described Christian socialist who drew little distinction between her Christianity and her socialism. “In Every Christian there exists a socialist; and in every socialist a Christian.” She was a president of the Woman’s Christian Temperance Union, which influenced the vision in “Looking Backward” of American socialism. Francis Bellamy, Edward’s cousin and another Christian socialist, wrote the Pledge of Allegiance. “Liberty and justice for all” pretty much epitomized the values behind his beliefs.

The modesty of socialist goals could ironically emerge as Mr. Sanders’s shield. Radicals — anarchists, Communists and other Marxists — have at critical moments influenced America’s development, often for the better, and most of them have despised American socialists as insufficiently revolutionary, ideologically incoherent, hopelessly sentimental and utterly enmeshed in existing society.

They were right — which was why American socialists have been far more influential than their radical critics. Socialists appealed to sensibility, values and justice, not ideologies. They put their hope in the benevolence and fairness of the mass of Americans —­ what Howells called the sufficiency of the common — rather than in elites. They often did not know exactly where they were going or how to get there, but they knew the direction they must go and who must accompany them. They did not despair. They seem quite familiar and quite American.