INDEPENDENCE, Mo. -- Business, meaning research by historians and nourishment for history hobbyists, is brisk at the Harry S. Truman Library on this 60th anniversary of the Berlin Airlift, the desegregation of the armed services, recognition of the state of Israel and the improbable election of the president responsible for many momentous policies. The library is a place, and now is a time, to ponder the transformation Truman wrought in the presidency and the Constitution, and why that transformation should be debated before the next president is selected.

With a mere 15 million pages of documents, this library is minuscule: The Clinton Library in Little Rock has 77 million pages. Presidential power has grown exponentially in the six decades since Truman augmented the national security apparatus responsive to the president by creating the National Security Council and the CIA. He, however, was crucial to the magnification of the president's war powers.

A 1948 photograph here shows Truman at a lectern delivering a campaign speech in Los Angeles. Seated near the lectern is the man who had introduced Truman, 37-year-old Ronald Reagan. Between Truman's and Reagan's presidencies, between the dawn and dusk of what John Kennedy called the Cold War's "long twilight struggle," Americans accepted extravagant -- or so the Founders would have thought -- assertions of presidential powers. These assertions have been made by presidents of both parties, but have been intensified by the current president in the context of "the long war" against terrorists.

At the 1787 Constitutional Convention, only one delegate (from ever-bellicose South Carolina, naturally) favored vesting presidents with an unfettered power to make war. Presidents, it was then thought, could respond on their own only to repel sudden attacks on the nation. "The Founders," says former Rep. David Skaggs, a Colorado Democrat, "counted on the competitive ambitions of the three branches to make checks and balances work." Instead, we have seen Congress' powers regarding war "migrate ignominiously to the executive."

A crucial event in the migration was Truman's decision to wage war in Korea, taken without Congress and never formally ratified by Congress, other than post facto by enabling appropriations, which are not an adequate substitute for the collaborative decision the Constitution's Framers anticipated for war-making. Since Korea, America has engaged in three major wars (Vietnam, Operation Desert Storm, Operation Iraqi Freedom) and many other exercises of military force, but Congress' constitutional powers relevant to war-making have atrophied from disuse. Both presidents Bush declared congressional assent unnecessary even while they were seeking it, in 1991 and 2002, respectively. Congress' passivity in the face of such constitutional impertinences has amounted to the silent repeal of the relevant constitutional provisions.

Because contemporary conservatism was born partly in reaction against two liberal presidents -- against FDR's New Deal and LBJ's Great Society -- conservatives, who used to fear concentrations of unchecked power, valued Congress as a bridle on strong chief executives. But, disoriented by their reverence for Reagan, and sedated by Republican victories in seven of the last 10 presidential elections, many conservatives have not just become comfortable with the idea of a strong president, they have embraced the theory of the "unitary executive."

This theory, refined during the Reagan administration, is that where the Constitution vests power in the executive, especially power over foreign affairs and war, the president, as chief executive, is rightfully immune to legislative abridgements of his autonomy. Judicial abridgements are another matter.

When in 1952 Truman, to forestall a strike, cited his "inherent" presidential powers during wartime to seize the steel mills, the Supreme Court rebuked him. In a letter here that he evidently never sent to Justice William Douglas, Truman said, "I don't see how a Court made up of so-called 'liberals' could do what that Court did to me." Attention, conservatives: Truman correctly identified a grandiose presidency with the theory and practice of liberalism.

It is but a brisk walk from the library, where Truman is buried, to the corner of Main and Maple Streets, where young Harry earned $3 a week cleaning bottles and mopping floors at Clinton's Drug Store. A few blocks away, a plaque marks where wagon trains formed for the Santa Fe, California and Oregon trails.

A lot started in this town, including, in a sense, an important facet of the modern presidency. That is an odd legacy for a man who is fondly remembered partly because he was, in all personal aspects, beguilingly free of pretense.