Corn's first book was a 1994 biography of longtime Central Intelligence Agency official Ted Shackley, which received mixed reviews. The book used Shackley's climb through the CIA bureaucracy to illustrate how the Agency worked and to follow some of its Cold War-era covert operations. In the Washington Post, Roger Warner called it "an impressive feat of research"; but, in the New York Times, Joseph Finder claimed Corn was seriously distorting history to blame Shackley for a series of CIA failings.

Corn moved on to fiction with a contribution to Unusual Suspects (1996), a paperback collection of crime stories published as a fundraiser to combat world hunger. His first novel, Deep Background, was a conspiracy thriller about the assassination of a President at a White House press conference and the ensuing investigation. Reviews praised Corn's mastery of the political atmosphere and characters, although they split on whether this was a virtue or, coming at the conclusion of the Clinton years, already all-too-familiar territory.

With the arrival of George W. Bush, Corn became a harsh critic of the President. His next book, The Lies of George W. Bush, charged that Bush had systematically "mugged the truth" as a political strategy; and he found fault with the media for failing to report this effectively. The book also broke with journalistic practice for its explicit charge of lying, a word usually avoided as editorializing.

In particular, Corn criticized many of the arguments offered to justify the 2003 Invasion of Iraq; and he challenged New York Times columnist William Safire for claiming links between Saddam Hussein and Al-Qaeda. In Hubris, written with Michael Isikoff of Newsweek, Corn analyzed the Bush administration's drive toward the invasion.

Corn was personally involved in the early coverage of the controversy over leaks to the media of the name of CIA officer Valerie Plame. After Robert Novak revealed Plame's identity in his July 14, 2003, column, Corn was the first to report, three days later, that Plame had been working covertly; and he raised the possibility that the leak of her identity violated the Intelligence Identities Protection Act.

Novak, for his part, disputed that Plame had been a covert operative at the time her identity was revealed. He also objected to the negative portrayal of himself in Hubris, for which he blamed Corn more than Isikoff. He said of Corn, "Nobody was more responsible for bloating this episode." Novak felt that Corn was too close with former ambassador Joseph Wilson, Plame's husband and a key figure in criticism of the administration's arguments for invasion.