Author Gore Vidal liked to call this country “the United States of Amnesia.” Even more so than other places, our country has been formed not by what it chooses to remember of its own past, but by what it chooses to forget.

In such a country, simply to remember is itself a radical act. It is to refuse to submit to the blinders that the powers that be are always trying to slip onto the rest of us. It is to subvert, implicitly or otherwise, the tyranny of the present — to insist on expanding the realm of the possible.

If all of this is true, then historian Eric Foner is one of the most dangerous men in the United States. And in the Trump era of sham populism turned shameless plutocracy, he might be the clearest voice on what this moment means for our country and how progressives might move forward.

The result is the American story told as more than just a series of isolated events. For example, Foner’s first contribution to the Nation 40 years ago was a article about the case of Sacco and Vanzetti, 50 years after the pair were executed. “The tragedy of their case,” he wrote, “lies not only in the injustice that was done but in the fact that their execution was one in a long train of events that seems to have driven their utopian vision out of American life.”

In 1993, Foner used the 130th anniversary of the Emancipation Proclamation to call for a “Third Reconstruction,” following the first one in the 1860s, which he had already written about so compellingly, and the second (the civil rights movement) in the 1960s. Nothing less was needed now, he wrote, than “a renewed national effort to address the racial divide that afflicts our society.” Yet such an effort would require “the kind of moral leadership and political courage this generation is unaccustomed to in its presidents.”

Within weeks of the 9/11 attacks, Foner wrote in the Nation that, “At times of crisis the most patriotic act of all is the unyielding defense of civil liberties, the right to dissent and equality before the law for all Americans.” He reminded us that our rights and liberties are not gifts from the state, but “the inheritance of a long history of struggles” by abolitionists, labor leaders, feminists and countless others whose “radical” beliefs in human freedom and dignity challenged an unjust system.

Similarly, in a 2015 open letter to Sen. Bernie Sanders (I-Vt.), Foner urged the presidential candidate to stop referring to Denmark as the inspiration for his democratic socialism and instead give credit to the United States’ own “radical forebears” — abolitionists, suffragettes, populists, Eugene V. Debs, the makers of the New Deal and the Great Society — and their fight for economic equality and social justice. These were uniquely American battles, grounded in uniquely American values.

Today, when we find ourselves in the hands of the most dangerously authoritarian and corrupt president in memory, it is this radical history that we are once again called upon to retrieve. And we are already seeing this in motion.

The day after Donald Trump’s poorly attended inauguration, millions of Americans across the country attended women’s marches in what was likely the single biggest day of political action in U.S. history. A few weeks later, Americans of all backgrounds spontaneously descended on airports across the country to protest Trump’s de facto Muslim ban. The past two weekends have seen scientists, activists, students and ordinary Americans march in Washington in defense of science and the fight against climate change.

This massive mobilization isn’t tied to one person or figure­head. It is an organic movement, with countless groups springing up to resist a president who would roll back 50 years of progress in equality, justice, and a fair economy. As Trump continues to weaken the federal government’s ability to regulate polluters and predatory finance, while pushing his sham populist, crony capitalist agenda, we should learn from our radical past. After all, as Foner has pointed out — and Trump’s bizarre comments about the Civil War reinforced — the president, too, is rooted in our history, from the Know-Nothings all the way to Nixon’s Southern strategy.

What the clashes of the past teach us is that we must stay committed to a cause bigger than any one person and be willing to fight for years to come. Above all, we must understand our “usable past” in order to reap its inspiration.