OPINION — There are times in American history when presidential leadership has made the difference between war and peace, or progress and decline.

Past American presidents have comforted the grieving, steeled the frightened, given courage to the wavering and championed the ideals of equality, liberty, strength and compassion. American presidents’ words across centuries have mattered because American leadership has mattered.

In 2001, six days after the attack on the World Trade Center, President George W. Bush offered a message of acceptance and tolerance when he went to the Islamic Center of Washington D.C. He called on all Americans to understand that “the face of terror is not the true faith of Islam.” Since his speech was broadcast live, Bush also declared to an international audience that America counts millions of Muslims as citizens and doctors, lawyers, law professors, members of the military, entrepreneurs, shopkeepers, moms and dads. “They need to be treated with respect,” he said. “In our anger and emotion, our fellow Americans must treat each other with respect.”

That was the kind of leadership in a national crisis that only a president could offer. Nobody other than the president could have called on individual Americans to embrace the Muslim community in the grief and anger following 9/11. The words of President Bush not only united the country, but also diffused the very real anger that grew up quickly after the attacks. He may even have saved lives at a time when the country could not bear more.

Two decades earlier, President Ronald Reagan spoke to the convention of the NAACP after a series of hate crimes against African-Americans broke out across the country. “A few isolated groups in the backwater of American life still hold perverted notions of what America is all about,” Reagan told the group. “To those individuals who persist in such hateful behavior … you are the ones who are out of step with our society. You are the ones who willfully violate the meaning of the dream that is America. And this country, because of what it stands for, will not stand for your conduct.”

Reagan and the NAACP were hardly political allies. But on the questions of bigotry and human dignity, Reagan and the NAACP were one.

Of course, political leadership and messages of unity don’t come only from presidents. Sometimes, they come from the defeated candidate or party. Sometimes they must. On the day that the Supreme Court decided Bush v. Gore in favor of the Texas governor, Vice President Al Gore conceded and told his supporters to do the same.

“Now the U.S. Supreme Court has spoken. Let there be no doubt, while I strongly disagree with the court’s decision, I accept it. I accept the finality of this outcome,” he said.

There was nothing that Bush could have said, even as the president, that could have been as effective as Gore’s public acceptance of the Supreme Court’s decision, even when he disagreed with it, and especially when it finalized his own defeat. But putting the country’s needs ahead of one’s own is the core of the nature of leadership.

Watch: Trump’s Tempered Tone Erased by Early Morning Tweet

Different times

Sometimes I wonder what students and scholars will quote from President Donald Trump’s cannon? Which moments of leadership or unifying rhetoric will we look back on to see him rising above the partisan and the personal to give the country the faith it looks for, particularly in a crisis?

Will it be his tweets calling half a dozen different African-Americans “low IQ?” Or refugees “invaders?” Or Democrats “funded by George Soros?”

Or maybe it will be his response last week to a serial bomber in Florida sending explosive devices to more than a dozen targets — all critics of President Trump. Instead of offering comfort to the would-be victims or assurance to the nation, the president’s first comments were to defend himself on Twitter: “Funny how lowly rated CNN, and others, can criticize me at will, even blaming me for the current spate of Bombs and ridiculously comparing this to September 11th and the Oklahoma City bombing, yet when I criticize them they go wild and scream, ‘it’s just not Presidential!’”

Or maybe it will be the president’s words Saturday, when a synagogue in Pittsburgh was horrifically attacked, killing 11 congregants. The first message out of the White House was a tweeted real-time update of the massacre as it played out on cable news. “Beware of active shooter. God Bless All!”

Later that night, as the president campaigned in Illinois and went back to Twitter to reiterate that the media were “the enemies of the people,” a video clip of a presidential speech about America’s refusal to tolerate bigotry ever again went viral on social media. The message was clear, direct and unambiguous and seemed to be the words the country needed to hear most in the face of the worst anti-Semitic attack in our history.

But the video was not of Trump, but of Reagan at the NAACP convention in 1981, telling hate groups, “You are the ones who are out of step with our society. You are the ones who willfully violate the meaning of the dream that is America. And this country, because of what it stands for, will not stand for your conduct.”

We know what America stands for. When will the president show us that’s what he stands for too?

Roll Call columnist Patricia Murphy covers national politics for The Daily Beast. Previously, she was the Capitol Hill bureau chief for Politics Daily and founder and editor of Citizen Jane Politics. Follow her on Twitter @1PatriciaMurphy.