The better presidents do not cater to such mobs; they conquer them with a breadth of vision that speaks to the best parts of our soul. None of those men was without fault. For generations the Democratic Party was home to many of the most strident segregationists, particularly from the South. For the past half century, too many Republicans have used coded racial appeals to win votes, often in the South as well. Still, they — and we — have also had the ability to rise above their baser impulses.

As Father Charles Coughlin, the populist and anti-Semitic radio priest, showed us, radio could have been a divisive force. Observers saw as much at the time. Lawrence Dennis, a Southerner and a former Foreign Service officer, argued in a pair of books in the 1930s that radio and other mass media made Americans susceptible to suggestion. “We have perfected techniques in propaganda and press and radio control which should make the United States the easiest country in the world to indoctrinate with any set of ideas, and to control for any physically possible ends.”

Which was why Roosevelt’s appeals to what Abraham Lincoln had called “the better angels of our nature” proved so essential. He did not broadcast solely for partisan purposes; he believed that greatness would come — to the country and, not coincidentally, to himself in the eyes of history — if he built beyond his base rather than simply speaking to it.

The television era offered similar perils and promise. In the 1950s observers fretted that presidential candidates were now being marketed like soap, but as the years passed it became clear that visual media had an extraordinary power to unify, if only for a time. Both Kennedy and Reagan understood the dramatic possibilities of the presidency-as-production, turning their hours upon the stage into national sagas. “There have been times in this office,” Reagan said as he left the White House, “when I’ve wondered how you could do the job if you hadn’t been an actor.”

Great performers, of course — and Reagan was one, as was his Cold War colleague John Paul II, who trained in the theater as a young man — present visions of a world beyond the tactile to their audiences. “I’ve spoken of the shining city all my political life, but I don’t know if I ever quite communicated what I saw when I said it,” Reagan said in his Farewell Address in 1989. “But in my mind it was a tall, proud city built on rocks stronger than oceans, windswept, God-blessed and teeming with people of all kinds living in harmony and peace; a city with free ports that hummed with commerce and creativity.”

It’s easy to be cynical about, and dismissive of, such a view. But, as G. K. Chesterton observed after a 1921 tour of the United States, America is “the only nation in the world founded on a creed” — and if natives and newcomers alike can live up to that creed of inclusion, then our best instincts will carry the day. As a matter of observable fact, the United States, through its sporadic adherence to that creed, is the most far-reaching and successful experiment in pluralistic republicanism the world has ever known. In the main, the America of the 21st century is, for all its shortcomings, freer and more accepting than it has ever been. If that weren’t the case, populist attacks on immigrants and the widening mainstream wouldn’t be so ferocious.

Perhaps borrowing from Henry David Thoreau, President Roosevelt added the most enduring line from his first inaugural address while at work on the speech at the Mayflower Hotel in the first days of March 1933. “The only thing we have to fear,” he wrote, “is fear itself.” Such sentiments are tweetable — one can say a lot in 280 characters — but they have to be deeply held by the one doing the tweeting.