In its timing, authorship and style of reporting, the book is strikingly reminiscent of the one Mr. Corsi wrote with John O’Neill about Mr. Kerry, “Unfit for Command,” which included various accusations that were ultimately undermined by news reports pointing out the contradictions. (Some critics of Mr. Kerry quoted in the book had earlier praised his bravery in incidents they were now asserting he had fabricated; one had earned a medal for bravery in a gun battle he accused Mr. Kerry of concocting.)

But books like “Unfit for Command,” which remained for some 12 weeks on the Times best-seller list, and, now, “The Obama Nation,” have become an effective and favored delivery system for political attacks. There have been anti-Clinton (both Bill and Hillary) and anti-Bush books too numerous to name. The sensational findings in these books, true or dubious, can quickly come to dominate the larger political discussion in the news media, especially on cable television and the less readily detectible confines of talk radio and partisan Web sites.

Fact-checking the books can require extensive labor and time from independent journalists, whose work often trails behind the media echo chamber.

Web sites on the left have begun poring over Mr. Corsi’s latest book. Media Matters, which is run by David Brock, a former right-wing journalist who wrote a classic of the attack genre, “The Real Anita Hill,” has been particularly aggressive in fact-checking the book, and its press releases on inaccuracies in the book have gotten some attention on cable television.

Several of the book’s accusations, in fact, are unsubstantiated, misleading or inaccurate.

For instance, Mr. Corsi writes that Mr. Obama had “yet to answer” whether he “stopped using marijuana and cocaine completely in college, or whether his drug usage extended to his law school days or beyond.” “How about in the U.S. Senate?” Mr. Corsi asks.

But Mr. Obama, who admitted to occasional marijuana and cocaine use in his high school and early college years, wrote in his memoir that he had “stopped getting high” when he moved to New York in the early 1980s. And in 2003 The State Journal-Register of Springfield, Ill., quoted him responding to a question of his drug use by saying, “I haven’t done anything since I was 20 years old.”