WASHINGTON (AP) — The U.S. intelligence chief, James Clapper, said this week that the loss of state secrets as a result of leaks by former National Security Agency analyst Edward Snowden was the worst in American history. Clapper backed up his assertion with dire forecasts about emboldened enemies abroad, but some historians and researchers said the U.S. has struggled with even more devastating intelligence breakdowns over the past century.

Clapper, the director of national intelligence, has said Snowden’s disclosures and the resulting media coverage are giving away blueprints for surveillance programs. “Terrorists and other adversaries of this country are going to school on U.S. intelligence sources, methods and tradecraft,” he told the Senate Intelligence Committee on Wednesday.