As a vision, it was bold and improbable—but the magazine these men launched that November, 160 years ago, helped spur the nation to redefine itself around the pursuit of the American idea. And as the United States grew and prospered, other peoples around the globe were attracted to its success, and the idea that produced it.

Now, though, the idea they articulated is in doubt. America no longer serves as a model for the world as it once did; its influence is receding. At home, critics on the left reject the notion that the U.S. has a special role to play; on the right, nationalists push to define American identity around culture, not principles. Is the American idea obsolete?

From the first, the idea provoked skepticism. It was radical to claim that a nation as new as America could have its own idea to give the world, it was destabilizing to discard rank and station and allow people to define their own destinies, and it bordered on absurd to believe that a nation so sprawling and heterogeneous could be governed as a democratic republic. By 1857, the experiment’s failure seemed imminent.

Across Europe, the 19th century had dawned as a democratic age, but darkened as it progressed. The revolutions of 1848 failed. Prussia busily cemented its dominance over the German states. In 1852, France’s Second Republic gave way to its Second Empire. Spain’s Progressive Biennium ended in 1856 as it began, with a coup d’état. Democracy was in full retreat. Even where it endured, the right to vote or hold office was generally restricted to a small, propertied elite.

On the surface, things appeared different in Boston, where The Atlantic’s eight founders—Emerson, Lowell, Moses Dresser Phillips, Henry Wadsworth Longfellow, John Lothrop Motley, James Elliot Cabot, Francis H. Underwood, and Oliver Wendell Holmes Sr.—dined in May 1857. Almost all adult males in Massachusetts, black and white alike, could vote, and almost all did. Almost all were literate. And they stood equal before the law. The previous Friday, the state had ratified a new constitutional amendment stripping out the last significant property qualifications for running for state Senate.

But even in Boston, democracy was embattled. The state’s government was in the grip of the nativist Know-Nothings, who resented recent waves of immigrants. That same Friday, voters had ratified an amendment imposing a literacy test for voting, a mostly symbolic effort at exclusion. But slavery, the diners believed, posed an even greater threat to democracy. Most of them had been radicalized three years before by the Anthony Burns case, when federal troops marched into their commonwealth to return Burns, an escaped slave then living and working in Boston, to bondage in Virginia—inspiring protests and lethal violence on his behalf. To the west, Kansas was bloodied by fighting between pro- and antislavery elements; to the south, politicians had begun defending slavery not as a necessary evil but as a positive ideal.