“If I were writing ‘The Vital Center’ today, I would tone down the rhetoric,” Mr. Schlesinger wrote in his memoir, “A Life in the 20th Century,” published in 2000. But that rhetoric was attuned to its moment. (The phrase “age of anxiety,” for instance, was the title of an eclogue by W.H. Auden, published in 1947.) And the “hortatory lushness” Mr. Schlesinger rued in his memoir suited the case he was trying to make for a new political alliance between liberals and conservatives who “believe deeply in civil liberties, in constitutional processes and in the democratic determination of political and economic policies.”

Today these seem self-evident virtues, but Mr. Schlesinger was writing in the immediate aftermath of World War II, with its fresh memories of Nazi death camps, its ongoing spectacle of Soviet brutalities and the new threat of nuclear annihilation. Mr. Schlesinger’s argument that, amid these perils, democracy could not be passively accepted as a national birthright but must be struggled for reflected the emerging mood of the country. His work presaged the civil rights protests of the next two decades even as it expressed the national yearning for a new kind of politics divorced from totalizing extremism.

All this would have made for a fine polemic. But the power of the book radiates from Mr. Schlesinger’s knowledge of modern history, American and European — in his concise but learned discussions of the Federalists, Whigs and Progressives and also of the roots of Communism and Fascism. This ability to find latent connections between the present and the past, as well as between American and Continental thinkers, elevated “The Vital Center” above the ranks of articulate manifestoes and placed it in the company of other monitory classics written at more or less the same cold war moment, including George Orwell’s “1984,” Hannah Arendt’s “Origins of Totalitarianism,” Whittaker Chambers’s “Witness” and Reinhold Niebuhr’s “Irony of American History.” (I should note here that Mr. Schlesinger favorably reviewed my biography of Chambers in The New York Times Book Review.)

That the phrase “vital center” has become a catchword for Democratic Party strategists intent on capturing the mainstream electorate attests to Mr. Schlesinger’s gift for phrase-making — a gift capitalized on by politicians like Adlai Stevenson, whose campaign he worked on.

But the phrase’s popularity also suggests that he wrote with an authority not to be found among younger historians and political thinkers, who continue to borrow from their elders. Peter Beinart, the former editor of The New Republic, has repeatedly invoked the vital center — the term but also the book — in magazine articles and in his own recent book, “The Good Fight.” Indeed, his book is patently an homage to Mr. Schlesinger’s.