Cambridge, Mass. ? He never so much as ran for sheriff, but he shaped the way two generations of Americans looked at politics. He was an adviser to presidents and, perhaps more important, an adviser to Americans about how to look at the presidency. He was Richard E. Neustadt, and his death the other day at age 84 seemed to mark an important but unnoted passage in American politics.

Mr. Neustadt was a quiet man with a rollicking laugh. He had a mastery of American political history and a gentle approach to his craft. He taught one of the great courses in American campus life, and legions of his students at Columbia and Harvard left his lectures with new understanding about the presidency, new intensity about politics, new idealism about the purpose of civic life. He was a teacher and, what is more, a teacher’s teacher.

I heard him lecture only once, on a November morning in 1986, a decade after my own college studies had ended. The Iran-Contra scandal was just then unfolding, and so new a part of the political landscape that it hadn’t yet acquired a name. Mr. Neustadt was a longtime believer in what he called the “foolish things” presidents do in their second terms — a warning to President Bush, should he have the chance — and this episode, so comic, so unnecessary, so inexplicable even now, was perfect fodder for a lecture on “the problem of balancing presidential advisers.”

Mr. Neustadt was then 67 years old, at the height of his powers intellectually, though perhaps not politically; he had worked in Harry Truman’s White House, helped John F. Kennedy with his presidential transition, was on call for Lyndon B. Johnson for the birth of the multilateral North Atlantic Treaty Organization force, and assisted Jimmy Carter with the organization of the White House staff. His “Presidential Power” was on every politico’s bookshelf, and on some presidents’, too. He was giving his course for the last time, and it was clear from one of the back seats of the lecture hall in Cambridge’s Arthur Sackler Museum that this man was still taken with — no, make that obsessed with — what he called “the power problem of the man inside the White House.”

Today the man inside the White House has a power problem, just like all of his predecessors, and if Mr. Neustadt were around he might say that President Bush has a management challenge, what with Condoleezza Rice and Donald Rumsfeld fighting even as the fighting continues in a far less mannerly setting halfway across the world in Iraq. Mr. Neustadt had an eye for irony, and he would view this situation as a feast for the eye.

He was armed with great impishness but also with great insight. “He was the first to understand that presidential power was not simply about the formal authority of the office but how presidents use that authority and marshal their resources,” Robert B. Reich, a former labor secretary, said just the other evening in a phone call full of reminiscences and regret. “He looked at the sociology of the presidency in ways that no scholar had before. He redefined the meaning of presidential power.”

Mostly he understood that power had many forms, and it was only last week that I discovered that Mr. Neustadt understood that presidential power sometimes outlived the president himself.

This insight is tucked inside a book that does not even bear Mr. Neustadt’s name. It is in the final paragraph of a new biography of Franklin Delano Roosevelt by Roy Jenkins, the British politician and writer. It turns out that Mr. Jenkins and Mr. Neustadt, besides admiring each other professionally, were also great friends, and when Mr. Jenkins died before completing the book, his widow, Dame Jennifer Jenkins, asked Mr. Neustadt to complete the book.

He did, of course, and the result is a seamless continuation of Mr. Jenkins’ manuscript. But that last paragraph is pure Neustadt, and it is pure genius:

With more than half a century’s perspective, it is evident that Roosevelt made a deep dent on his times; another six months or so might have made the dent a bit deeper. Regardless, from our long perspective one thing seems very clear: the Big Three of the Second World War stand very differently in history. The world we now live in is not Churchill’s, with its vanished British Empire, and not Stalin’s, with his Soviet Union but a memory, his tyranny fully exposed, and Communist parties dethroned save in Cuba, or immensely reshaped as in China. The world we live in is still Franklin Roosevelt’s world, more fragmented yet with population doubled, weapons and communications revolutionized, dangerous in new ways, but essentially recognizable. For good or ill, the United States is at its center, as it came to be in his time, and the presidency is at the center of its government, a position he restored and fostered. His story and he remain vital to the darkened future.

That paragraph is as perfect a piece of historical perspective ever written, besides being a remarkable example of the artful use of the comma, and the knowing, amplifying aside. I used to say that it was possible to understand American politics by knowing only 10 people, as long as one of the 10 were Richard Neustadt. To this day I know his phone number by heart. The tragedy is that he is not here to answer.

David Shribman is a columnist for the Pittsburgh Post-Gazette.