That night, the mob broke into the prison, killed one journalist and left the others for dead. When the mob leaders were brought before a jury, they were acquitted.

Alexis de Tocqueville tells this chilling story in "Democracy in America," and warns that the greatest threat the United States faces is the tyranny of the majority, a phrase he is credited with coining. His account of his travels through America in the 1830's, which is often called the greatest book ever written about America, is both an appreciation of American democracy, and a cautionary tale about its fragility.

Bernard-Henri Lévy, the well-known French intellectual, has just written "American Vertigo," about his own travels along Tocqueville's route. It is an entertaining trip, as much in the tradition of Jack Kerouac as Tocqueville. Mr. Lévy visited Rikers Island and a Dallas gun show, and interviewed Americans ranging from Richard Perle to Sharon Stone. His outsider's perspective sometimes lends insight, as with his reflections on the sad plight of Detroit and Buffalo. At other times, it just leads to odd advice. (He puts surprising faith in Warren Beatty as a political leader.)

Unfortunately, Mr. Lévy, who is most passionate about American foreign policy, pays little attention to the issue Tocqueville was most intent on: how closely even a thriving democracy like America borders on tyranny. It is a subject that is particularly relevant today, with the president claiming he can wiretap ordinary Americans without a warrant, insisting on his right to imprison without trial anyone he labels an "enemy combatant," and warning critics of the Iraq war against "emboldening" the enemy. Entertaining as Mr. Lévy's book is, "Democracy in America" - 170 years old, and notoriously difficult to distill - still provides far greater insight into contemporary American democracy.

Tocqueville, who was born into the French aristocracy, was just 25 years old when he landed in Newport, R.I., in 1831 with the professed aim of studying the American penal system. In his travels, he visited prisons, but he also interviewed important personages, including President Andrew Jackson, former president John Quincy Adams and Supreme Court Justice Joseph Story.

The book Tocqueville produced - a first volume published in 1835, and a more somber one five years later - is full of keen observations about America. Many are highly quotable. ("There is hardly a political question in the United States which does not sooner or later turn into a judicial one.") Some are merely durably accurate. ("The most outstanding Americans are seldom summoned to public office.")

Tocqueville is hard to place on the modern political spectrum. He was raised in a royalist family that suffered mightily in the French Revolution: his grandfather and an aunt were guillotined, and his parents nearly suffered the same fate. He brought to his study of American democracy - which he was transmitting back to Europe, where democracy was on the march - the fear that democracy combined with a strong central power could lead to tyranny.

It was a very different America that Tocqueville was writing about in the Jacksonian Age, but the concerns he raised still resonate strongly. He worried that the state's power would end up concentrated in a single authority, until its citizens were "reduced to nothing better than a flock of timid and industrious animals, of which the government is the shepherd." He feared the majority would trample on minorities, like the mob that attacked the Baltimore editors, or the whites of Pennsylvania who intimidated blacks into not voting. And he was concerned about tyranny of opinion, saying he knew of no country with "less independence of mind and true freedom of discussion" than America.

Tocqueville pointed to some bulwarks against tyranny. He was a firm supporter of checks and balances. He believed in the power of American law to limit the excesses of the ruler - the exact issue in today's debate over the warrantless wiretapping of American citizens. He had great hopes for the judiciary. "The courts correct the aberrations of democracy," he wrote, and "though they can never stop the movements of the majority, they do succeed in checking and directing them." Tocqueville would not be surprised that the Supreme Court has limited the Bush administration's excesses in the war on terror - or that the administration has been eager to nominate justices with an expansive view of presidential power.

Tocqueville would not have been distracted by all the talk that warrantless wiretaps, indefinite detainment of enemy combatants and other civil liberties incursions are serving the cause of freedom. He understood that the newest incarnation of despotism was likely to be ushered in by the "avowed lover of liberty" who is a "hidden servant of tyranny."

Nor, though, would he be likely to despair. One reason "Democracy in America" has remained so popular is that despite his fears, Tocqueville remained nervously optimistic about democracy. He knew that the kind of equality that had taken hold in America could lead to tyranny, but he also believed that it gave people a "taste for free institutions," which would lead them to resist. Equality "insinuates deep into the heart and mind of every man some vague notion and some instinctive inclination toward political freedom," he insisted, "thereby preparing the antidote for the ill which it has produced."