When Sen. John McCain spoke during an Armed Services Committee hearing last year on security issues in the Western Hemisphere, he relayed a stark warning about the spread of Mexican drug cartels in the United States. "The cartels," the Arizona Republican said, "now maintain a presence in over 1,000 cities."

McCain based his remarks on a report by a now-defunct division of the Justice Department, the National Drug Intelligence Center (NDIC), which had concluded in 2011 that Mexican criminal organizations, including seven major drug cartels, were operating in more than 1,000 U.S. cities.

But the number, widely reported by news organizations across the country, is misleading at best, according to U.S. law enforcement officials and drug policy analysts interviewed by The Washington Post. They said the number is inflated because it relied heavily on self-reporting by law enforcement agencies, not on documented criminal cases involving drug trafficking organizations and cartels.