Say what you will about the sins of the Bush Administration. But credit it with one small but welcome accomplishment: It has moved Arthur Schlesinger Jr. to give a vigorous lesson about the peril of keeping an arrogant moralist in the White House. The great liberal historian made his name by writing long, sympathetic, popular books about great liberal politicians: The Age of Jackson, The Age of Roosevelt, A Thousand Days, Robert Kennedy and His Times. Meanwhile, Schlesinger was never shy about making some history himself; he helped found Americans for Democratic Action, advised Adlai Stevenson’s campaigns for President and was a special assistant in the Kennedy White House. At 86, he remains a passionate liberal who is friendly with leading Democrats and is eager to point out the follies of the Bushian right.

Yet, away from the bestseller lists, Schlesinger has often been a counselor of caution–about the twin dangers of breakneck ideology and unrivaled power. His cold war classic, The Vital Center, urged fellow liberals to resist Stalinism with as much fervor as they spurned the anti-Communist right. The Imperial Presidency, published just as Watergate became a crisis, stuck a lasting name on the grab for supremacy by the executive branch. And in The Disuniting of America, Schlesinger took radical multiculturalists to task for viewing American nationalism as little more than a device for the oppression of ethnic minorities.

His books, always written with supreme confidence and arresting prose, have seldom found favor in the pages of this magazine. Most leftists wrote off Schlesinger as the court historian of the liberal establishment, at least when such an animal truly existed. But his most thoughtful and provocative work has always been critical of dogmatic and domineering officeholders rather than a tribute to liberal heroes. Inspiring much of that writing is the ironic judgment Schlesinger learned from his friend, the theologian Reinhold Niebuhr: Moralists who divide the world between absolute evil and spotless virtue usually impede the progress of the good. As Niebuhr wrote, smack in the middle of the Korean War and at the height of McCarthyism, “A too confident sense of justice always leads to injustice.”

How apt that sounds half a century later. The debacle in Iraq provides, for Schlesinger, a perfect illustration of why would-be messiahs make bad Presidents. Based on intelligence that was little more than a compilation of wishful thinking, George W. Bush went to war for an idea–that “converting the Arab world to representative democracy” was both feasible and right. In so doing, he made a radical change in the doctrine of American foreign policy. Instead of containing and deterring potential enemies, as during the cold war, Bush declared that the United States had a duty to make war so that others would not do the same.

Schlesinger delivers this now-familiar indictment with a dash of wit. He compares Dick Cheney and Donald Rumsfeld to the relentless “precogs” in Steven Spielberg’s Minority Report, who can “see” crimes and stop them before they occur. But, writes Schlesinger, “in the real world, preventive war depends on accurate intelligence, which is all too often unavailable, supplemented by dubious historical analogies.” The Bush team imagined the invasion of Iraq would look like the liberation of France or Italy near the end of World War II; instead, it stirs memories of Vietnam.

Although there’s nothing particularly original about Schlesinger’s argument, he does ground it in a more sober historical critique than most antiwar critics have offered. Unilateralism, he points out, is a venerable tradition in US foreign policy. Until World War I, George Washington’s doctrine of no “permanent alliances” governed America’s relationships with the outside world. Woodrow Wilson broke the habit of going it alone when he sought to pin the nation’s security to a powerful League of Nations. But his own unbending moralism sabotaged the enterprise, and it wasn’t revived until the 1940s, when the more pragmatic FDR converted a wartime alliance into the United Nations, and Harry Truman mobilized the anti-Soviet governments of Europe into NATO.

In contrast, George W. Bush harks back to those nineteenth-century Presidents who believed America should act only by itself and for itself. Yet, at the same time, he longs to convert the world to freedom, Republican style. No wonder his precog war has been such a disaster.

Useful as they are, Schlesinger’s reflections are not honest enough about the past. The scholar who did much to glorify the Kennedys still views the historical record with the blinders of a partisan. He fails to reckon with the preventive, unilateral battles that liberal Democrats fought in the name of defeating Communism. Schlesinger neglects the proxy invasion of Cuba at the Bay of Pigs (which, as a White House official, he warned against) and glosses over the war in Indochina, which most US allies opposed and which neither JFK nor Lyndon Johnson asked the UN to sanction. Only in Europe did American policy-makers really work in partnership with like-minded leaders. And that alliance succeeded only because its adversaries in the Soviet bloc were fast losing the allegiance of their own people. The reality in Cuba and Vietnam was quite different; even many foes of state socialism regarded Ho Chi Minh and Fidel Castro as authentic fighters for national independence.

Other essays in this little book go beyond the pitfalls of going it alone. Schlesinger issues a rebuke to those who would stifle dissent in wartime. He shows that, from John Adams’s Sedition Act to John Ashcroft’s Patriot Act, such measures fail to achieve their ends and make their architects look nasty in the light of history. Less cogent is an essay that proposes an overly complex scheme to replace the Electoral College. Yet another makes the unremarkable observation that, in the sweep of world history, democracy is a young form of government that is now imperiled by “religious fanaticism” and “the politics of identity.” Like most op-eds, such pieces are not likely to change many minds or hold their value for long.

Fortunately, the citizen-scholar saves his best thinking for last. After surveying the errors of policy-makers, past and present, Schlesinger asks, “What use is history anyway?” His answer is a nugget of good sense. Historians are neither useful for predicting the future nor for reducing the past to a single, overriding variable–be it class struggle, religious faith or the advance of free markets. What they can do is to explain why an empire faltered or a revolution turned dictatorial–and point to features of those events that often recur, although the details of each case cannot.

His larger point echoes what Niebuhr preached and Isaiah Berlin argued in his luminous, if repetitive, studies in intellectual history: Those who believe they have found the key to history inevitably lose their way in a swamp of self-righteousness, from which tyranny grows. Leftists who dismiss this as a refusal to take sides fail to realize that irony remains an essential tool for an American political historian. Because our nation’s ideals are so audaciously universalist and transcendent, they will always disappoint, even anger those who take them seriously.

Schlesinger concludes, “History should lead statesmen to a profound and humbling sense of human frailty–to a recognition of the fact, so insistently demonstrated by experience and so tragically destructive of our most cherished certitudes, that the possibilities of history are far richer and more various than the human intellect is likely to conceive.” That wisdom, he quickly adds, does not relieve us “from the necessity of meeting our obligations.” The last word is undefined, perhaps to indicate its moral complexity. Schlesinger, who is writing the second volume of his memoirs, has not retired from the craft of history writing. But those sentences should endure as a fitting epitaph for a life of often profound, always contentious work.