“American history is vanishing before our eyes,” says Bruce Watson, author of the new Sacco and Vanzetti: The Men, the Murders, and the Judgment of Mankind (Viking). “I did a survey of history books — about 16 of them, high-school and college level. At the most, they have a paragraph or two on this case. A couple didn’t have it at all.”

This Thursday, August 23, marks 80 years since the Italian-born anarchists, after a joint trial marred by anti-immigrant and anti-radical bias, were electrocuted in Charlestown Prison for a double murder committed in the course of a robbery.

The anniversary will be marked this week by the Sacco and Vanzetti Commemoration Society with a march from Copley Square to the North End on Thursday at 3 pm; a night of music, poetry, and theater at the Community Church of Boston on Friday at 7 pm; and the screening of two documentary films — Peter Miller’s 2006 Sacco and Vanzetti and David Rothauser’s 2004 The Diary of Sacco and Vanzetti — at Encuentro5, at 33 Harrison Avenue, on Saturday at 7 pm.

If few people think about Sacco and Vanzetti these days, it’s worth remembering that, “by the time of their execution, they were the most famous men in the world,” says Watson. Such was the global outrage at their deaths.

Watson’s book is especially valuable for its evocation of the men’s characters. Vanzetti was “very eloquent,” someone “any academic bookish person would fall in love with,” he says. Sacco “seemed much more innocent and naive than Vanzetti, but at the same time he . . . had a temper, and was every bit as radical, politically.”

And make no mistake, both men were ardent anarchists. Watson concludes that “they had probably been involved [with], or at least knew the guys” who devised a nationwide 1919 mail-bomb campaign. And “that, of course, opens the question of would they have done the robbery.”

Says Watson, “I think the preponderance of evidence certainly points toward innocence. There certainly was a reasonable doubt, but the jury ignored that.”

Still, there are “nagging doubts” that the two defendants may indeed have killed shoe-factory paymaster Frederick A. Parmenter and security guard Alessandro Berardelli, Watson allows. “But you’d have to convince me a lot more. The character of the men is such that it just doesn’t fit the crime.” (Some historians have posited that Sacco was guilty, but Vanzetti was innocent.)

Whatever their culpability, it’s inarguable that the pair did not receive a fair trial. Beyond being tainted by virulent anti-Italian bias and a revulsion of the defendants’ radical politics, the 1921 conviction took place in a country preoccupied by the xenophobic aftermath of World War I, the devastating tragedy of the 1918 flu epidemic, and the Red Scare — a state of itchy unease only exacerbated by Prohibition.

Compare that with the post-9/11 mood: the paranoia and seething partisan rage, the governmental furtiveness and trumped-up trials, the rabid anti-immigrant sentiment.

Ours is a country where a citizen, Jose Padilla, can be imprisoned for three-and-a-half years without being charged or provided legal counsel, just by being labeled an “enemy combatant”; a country where Newt Gingrich rails that “young Americans in our cities are [being] massacred” by illegal immigrants.

In times of crisis, Watson says, there’s a presumption of guilt rather than of innocence, a tendency toward surreptitious power plays. “These things are human traits, I’m afraid, especially in an era after a huge attack, as we had after 1919, and after 9/11.” The fear of anarchists and Italians, then, has simply been transposed eight decades later to Muslims and Mexicans.

And reading the words of one of Sacco and Vanzetti’s attorneys, William Thompson, it’s hard not to think of the current regime: “A government which has come to value its own secrets more than it does the lives of its citizens has become a tyranny, whether you call it a republic, a monarchy, or anything else.”

If the legacy of Sacco and Vanzetti is fading fast, that aspect of their story, at least, is not vanishing fast enough.