PRESIDENTS HAVE LONG LED WITH SENSITIVITY

degrees of success, to summon Americans to a higher moral purpose.

Abraham Lincoln, in his second inaugural address, called on Americans, bitter after years of civil war, to bind up their wounds “with malice toward none; with charity for all; with firmness in the right.”

Theodore Roosevelt spoke from a bully pulpit about the need to shield the vulnerable from the predations of industry. Woodrow Wilson prayed that World War I would be the war to end all wars. Franklin D. Roosevelt, who enacted the New Deal and vanquished fascism in Europe and Japan, said the presidency was primarily a place for moral leadership.

“The presidency is a center of moral authority in this country,” said Robert Dallek, a historian who is publishing a biography of F.D.R. this fall. “Every president before Trump thought of it in this way.”

If anything, the president’s role as a moral arbiter has only deepened in recent decades, as American society has become more secular, more racially and ethnically diverse, and more atomized by the splintering of mass media and the rise of social media.

“Especially in modern times, with instant communications, many Americans are inclined to look to a president for guidance on what to think about crucial issues,” the historian Michael Beschloss said. “A president must always speak with an intense degree of moral sensitivity.”

When Jimmy Carter was asked in 1978 whether he planned to use the moral weight of his office to block American neo-nazis from marching in Skokie, Ill., a predominantly Jewish suburb of Chicago, he replied that it was up to the courts. But he added, “I wish that this demonstration of an abhorrent political and social philosophy would not be present at all.”

Ronald Reagan famously spoke of America as a moral lodestar — a “shining city on a hill.” In his farewell address in 1989, he said, “She’s still a beacon, still a magnet for all who must have freedom, for all the pilgrims from all the lost places who are hurtling through the darkness, toward home.”

George W. Bush, addressing Congress days after the terrorist attacks of Sept. 11, 2001, issued a call to arms against the Islamic extremists who brought down the World Trade Center. But he coupled it with an appeal to avoid a broader attack on Islam.

“We respect your faith,” Bush said. “It’s practiced freely by many millions of Americans and by millions more in countries that America counts as friends. Its teachings are good and peaceful, and those who commit evil in the name of Allah blaspheme the name of Allah.”

Trump’s predecessor, Barack Obama, appealed to the best in Americans through a heartbreaking succession of police shootings and racially motivated killings. He often invoked the notion of grace — never more indelibly than in Charleston, South Carolina, after a white supremacist gunned down nine people, all African Americans, during a prayer service at Emanuel African Methodist Episcopal Church.

“We don’t earn grace, but we choose how to receive it. We decide how to honor it,” Obama said, before leading a memorial service in the hymn “Amazing Grace.”

“Justice,” he said, “grows out of recognition, of ourselves in others; that my liberty depends on my respect for yours; that history must not be a sword to justify injustice, or a shield against progress, but must be a manual for how to avoid repeating the mistakes of the past.”

None of Trump’s predecessors lived up to the moral standards they set. Franklin Roosevelt interned 125,000 Japanese-americans during World War II. Bush’s war in Iraq inflamed America’s relations with the Islamic world. Obama, who spoke fervently about the need for the United States to intervene on humanitarian grounds in foreign conflicts — “inaction tears at our conscience,” he said in 2009 — failed to do so in war-torn Syria.

In some cases — Richard M. Nixon’s abuse of power and Bill Clinton’s personal transgressions — the moral shortcomings were great.

But until now, no president has rejected the very concept of moral leadership. On Saturday, in his first response to Charlottesville, Trump condemned the violence “on many sides.” Then he lapsed into the passive voice, expressing, as he has before, a sense of futility that the divisions between Americans would ever be healed.

“It’s been going on for a long time in our country,” he said. “Not Donald Trump, not Barack Obama. This has been going on for a long, long time.”