What did Franklin D. Roosevelt accomplish? It is vital to understand it now, as we Americans consider making fundamental alterations in his legacy. Essentially, he preserved and enlarged the promise of human freedom in our time. Or, as Joseph Alsop put it, “On a very wide front and in the truest possible sense, Franklin Delano Roosevelt included the excluded.”

It is difficult now to conceive of how different America and the world were when Roosevelt came to power – or how different they might have been had he not come to power. It was, in Arthur Schlesinger Jr.’s phrase, “a frightened age when the air was filled with the sound of certitudes cracking on every side.” No other American leader – not even Lincoln – has faced such complex and potentially lethal crises as the Great Depression and the Second World War.

The America of 1933, racked by four years of depression, was all but exhausted with democracy. Every bank in the country was in the process of closing its doors. Thousands of square miles of farmland had become a desert. Between one-quarter and one-third of the work force was unemployed, and millions were being evicted from their homes and their land every year.

The Depression was neither a natural catastrophe nor an isolated event. Things had never been quite so bad, but every 5 to 10 years, for the better part of a century, the country had suffered a wrenching economic collapse, much worse than any recession Americans have endured since World War II. Bank failures and Wall Street panics were common, and usually led to nationwide meltdowns.

Most elderly Americans lived in abject poverty. Working men and women worked six days a week, 12 to 16 hours a day. They were routinely joined at the job by their children; few people ever finished high school, let alone college.

A system of apartheid, rationalized by bad science and enforced by lynching, ruled in the South. Another system of quotas routinely kept blacks, women, Jews and ethnic whites out of the best jobs and schools.

Farmers could rarely make a living; more and more were reduced to the serfdom of share-cropping. Nine-tenths of rural Americans did not even have electricity.

The root causes of these conditions were basic, long-standing flaws in American democracy. More shocking than the conditions in which Americans of 1933 lived was how little say they had in anything that mattered. Banking and investment were dominated by a small circle of self-interested, often dishonest men. Politics in every large city was usually controlled by corrupt political machines. In the South, millions of blacks and poor whites were kept from the ballot box by poll taxes, literacy tests and force of arms.

The power of landlords and large corporations was rarely contained. Unions were small and powerless. The courts repeatedly struck down the most basic minimum wage, child labor, consumer protection and worker safety laws.

The Depression only brought these ongoing social crises to a head, yet few at the time saw more democracy as an answer. The very idea of democracy seemed to be outmoded in the swift and steely industrial world. Hard new nostrums abounded in the 1930s and ’40s: communism, fascism, socialism, technocracy, corporatism.

Liberal democracy—and Roosevelt—succeeded in their rough, inconsistent way because that is the way of the world. What Roosevelt possessed was the essential flexibility of mind for a democracy. It was indicative that during his first presidential campaign he promised above all “bold, persistent experimentation. It is common sense to take a method and try it. If it fails, admit it frankly and try another. But above all, try something.”

Not everything he tried worked well, and some things did not work at all, and many of the New Deal’s innovations have required revision. Roosevelt himself would have been baffled by the notion that they would not, for he was not erecting a Marxist utopia but a viable, modern democracy. What he did was to turn his entire administration into an ongoing debate on democracy. Roosevelt had everyone from Norman Thomas to John Maynard Keynes up to the Oval Office. “If one definition of genius is an infinite capacity to make use of everyone and everything,” wrote William Manchester, “then Roosevelt certainly qualified.”

Best of all, he extended this debate into the living rooms of every home in America. FDR gave the press unprecedented access to the White House, and there were the “fireside chats.” “As he talked, his head would nod and his hands would move in simple, natural, comfortable gestures,” Secretary of Labor Frances Perkins recalled of these radio addresses. “His face would smile and light up as though he were actually sitting on the front porch or in the parlor with them.”

His fireside chats were amazingly detailed lessons in how the country worked. Before reopening the failed banks during his first weeks in office, for example, he took to the airwaves to explain modern banking, and how it had been reformed: “I know that when you understand what we in Washington have been about I shall continue to have your cooperation,” he intoned with his usual grand confidence, and he was right.

Yet for all his democratic pragmatism, we look for something more. The life of Richard Nixon provides an example of what can come from expediency ungrounded in any deeper principle. Was there any guiding spirit, anything more to Franklin Delano Roosevelt than tactics and timing, to account for the great outpouring of grief 50 years ago?

There are at least two stories from his life that I think are telling. One was the account that he was unimpressed by the Grand Canyon: “It looks dead. I like my green trees at Hyde Park better. They are alive and growing.”

“He responded to what was vital, not to what was lifeless; to what was coming, to what was passing away,” wrote Mr. Schlesinger. “He lived by his exaltation in distant horizons and uncharted seas.”

The other story is from when he was first trying to win back some use of his legs after the attack of polio that crippled him. He would try, every day, to make it the quarter of a mile from his Hyde Park home to the post office on his crutches.

It was a torturous journey for a man with no working muscles from his hips down. Sometimes he would fall – and have to wait, lying face down in the road, for someone to come along and help him back up. “For better or worse, I believe that the Roosevelt who could not walk was in most respects very like the one who could,” writes Geoffrey Ward, and most current biographers would concur. It was Roosevelt’s strong, optimistic – and deceptive – character that got him through the loss of his legs to polio, and not the polio that built the character.

Yet what better training has any president had – in patience, in humility, in building a basic sympathy for the human condition? Franklin Roosevelt understood the clumsy, halting progress of us all, and nurtured it, and the American people loved him for it as they have loved few men since.