Former president Barack Obama’s 19-minute speech Wednesday night at the Democratic National Convention sounded a few familiar notes. There was the soaring idealism consistent with every major speech he has given since his 2004 convention keynote vaulted him to fame. There was his tribute to Joe Biden, whom he called “a brother”; his extolling the virtues of the American experiment in democracy, despite its imperfections; and his often stated faith in the notion that progress requires incremental gains made by ordinary Americans and their elected leaders, against overwhelming odds, to create a more perfect union.

But Obama also invoked something unusual for him: fear. He gave it a name — Donald Trump — and without uttering the word, he used it to urge Americans not to put fear out of their minds, as Franklin D. Roosevelt had in his 1933 inaugural address, when the reference was to irrational fear, but to recognize its all too real source and act.

Obama cast the incumbent president as an existential threat to democracy. “I did hope, for the sake of our country, that Donald Trump might show some interest in taking the job seriously, that he might come to feel the weight of the office and discover some reverence for the democracy that had been placed in his care,” Obama told the nation. “This administration has shown it will tear our democracy down if that’s what it takes to win.”

It’s not that Obama is the first former president to hold a successor in contempt, or to treat him as part of a fundamentally anti-democratic movement imperiling the very idea of national progress and democratic renewal. Former presidents have often found themselves spluttering in rage at the ideological peril embodied by the men who succeeded them. After Roosevelt defeated Herbert Hoover in 1932, Hoover began to advance the notion that “the New Deal was no mere error, but a dangerously alien program engrafted onto the American political system that would, if indulged, destroy and supplant its host,” as historian Eric Rauchway observed in “Winter War,” his book about the Hoover-Roosevelt feud during the transfer of power.

Hoover decried FDR’s New Deal agenda as “fascist” and “socialist.” The New Deal, he told the Republican Convention four years later, was leading the country to “the crippling and possibly the destruction of the freedom of men.” Like Obama’s fear-based message, Hoover’s was based on his vision of America. Unlike Obama, however, Hoover saw the country as a place where virtually any government economic intervention would twist the nation’s founding creed and push the country on a “march to Moscow.”

Obama’s five-alarm speech, in that sense, was no departure from post-presidential rhetoric, nor a break with a general refusal of ex-presidents to criticize successors in overt, strident terms. He had promised as much early in his post-presidency, when he vowed to speak up, to criticize the incumbent, if circumstances justified it. Clearly, he believes that we are faced with a national emergency.

In 1933, Roosevelt faced a different kind of national emergency: 25 percent unemployment, a Great Depression and a fear that democracy would die amid the rise of communist and fascist totalitarian movements. Roosevelt’s inaugural address featured his message that “the only thing to fear is fear itself — nameless, unreasoning, unjustified terror which paralyzes needed efforts to convert retreat into advance. In every dark hour of our national life a leadership of frankness and vigor has met with that understanding and support of the people themselves which is essential to victory. I am convinced that you will again give that support to leadership in these critical days.”

Obama’s speech employed fear as an urtext to speak directly to voters. Fear can be grounded in the reality of the moment, or it can be wielded as a weapon in ways divorced from conditions in the country. Obama’s use was rooted in the former, which is what imbued it with power. And he had good reason to evoke it. The more than 170,000 Americans who have died of covid-19; an unemployment rate of more than 10 percent; Trump’s inability to lead a coordinated national response to the pandemic; his attacks on science and medicine and his embrace of conspiracy theories — all of these, Obama justifiably argued, have combined to form a distinct threat to lives and livelihoods that heighten the election’s stakes.

But Obama’s argument for why Americans should fear four more years of Trump’s authoritarian rule rested on an even more fundamental claim — that democracy is in danger unless citizens exercise their most foundational right and vote in overwhelming numbers to remove Trump from office. Obama told Americans, in essence, to be afraid for their way of life. Trump has used his office to promote his brand, enrich himself and his friends, attack the news media as the “enemy of the people” (a phrase favored by Stalin) and, through his efforts to debunk the reliability of mail-in voting and defunding the United States Post Office, attempt to suppress the vote.

Fear, then, was something that Obama asked Americans to embrace, to move them to action. It is a staple of political oratory, one of the great motivators for voters heading to the polls, even if it has not been in Obama’s go-to repertoire until now. Indeed, large majorities of pro-Biden voters tell pollsters that their ballot will be more a vote against Trump than a vote for Biden — that fear of four more years of Trump is their greatest driving emotion.

On the night of the attack on Pearl Harbor, before FDR addressed the nation (“a day that will live in infamy”), Eleanor Roosevelt delivered a national radio address in which she acknowledged to the mothers of America that they were all afraid. “I should like to say just a word to the women in the country tonight. I have a boy at sea on a destroyer. For all I know he may be on his way to the Pacific. Two of my children are in coast cities on the Pacific. Many of you all over this country have boys in the services who will now be called upon to go into action. You have friends and families in what has suddenly become a danger zone. You cannot escape anxiety. You cannot escape a clutch of fear at your heart. And yet I hope that the certainty of what we have to meet will make you rise above these fears.”

Obama’s message echoed hers as much as her husband’s. He was asking Americans to be afraid of what Trump would do in a second term, but, in essence, to rise above those fears to be moved to action. His speech reflected a tradition of pragmatic liberalism, in which government is not evil but a democratizing force, helping to ensure the right to vote, equal treatment of all people regardless of race, sex, religion or country of origin, and curbing unrestricted big business and the wealthiest individuals to give a fairer shake to workers. This liberal tradition is under threat from Trump, and Obama made the case as well as anyone has that fear is a reasonable reaction to the chaos and lunacy on display every day in Trump’s White House.