ITHACA, N.Y. - In their new book, "Four Threats: The Recurring Crises of American Democracy," Suzanne Mettler, professor of government at Cornell University, and Robert Lieberman, professor of political science at Johns Hopkins University, not only assert that history repeats itself - they also identify the underlying causes of democracy destabilization. American democracy has often been fragile, they argue, and today it faces an unprecedented crisis.
Tensions between political sides had been rising for years. The president signed laws to keep out immigrants from so-called "hostile" nations and to prosecute those who criticized his administration. Party divisions spilled into everyday life, leading to fights and violence.
The reference is not, as a reader in today's America might think, to the present day. It was 1798, and President John Adams had just signed the Alien and Sedition Acts. The young nation faced the possibility that states would secede, aristocrats would take power, and the democracy, operating under a Constitution not yet a decade old, would collapse.
"Watching the growing chaos and division, Americans of all stripes worried that their experiment in self-government might not survive the decade," write Mettler and Lieberman.
Four threats weaken democracy: political polarization; conflict over who belongs in the political community; high and growing economic inequality; and excessive executive power. Each of these threats by itself can damage democracy, and "Four Threats" explores examples that include economic inequality in the 1890s combined with political polarization that led to the disenfranchisement of millions of African American men and the expansion of executive power in the 1930s during the Great Depression.
Now, Mettler and Lieberman argue in the book, America faces all four threats at the same time. Today's deep political polarization, race- and gender-based tensions, soaring economic inequality and expanded executive capacity have given rise to political leaders willing to circumvent established norms to gain, wield and keep power.
"It is this unprecedented confluence of all four threats - more than the rise to power of any particular leader - that lies behind the contemporary crisis of American democracy," they write. "The threats have grown deeply entrenched, and they will likely persist and wreak havoc for some time to come."
"Four Threats" details past crises not only to illustrate how democracy goes wrong, but also to identify factors that help democracy to thrive. From the same episodes of the past, we can learn that democracy works well in a society that is less polarized, more inclusive and where people in power are held accountable.
The book also describes how should remember that democracy is a work in progress and can change course. During one of the lowest points of American democracy - the Civil War - President Abraham Lincoln's Gettysburg Address called democracy an "unfinished work."
Mettler and Lieberman call on Americans to continue this work in progress. "With the spirit of magnanimity and shared citizenship invoked by Lincoln," they write, "let us carry on the work to strengthen and revitalize democracy."