Mexican drug cartels have displaced the mafia as the "number one organized crime threat" in the United States, Sen. Joe Lieberman said Monday as his Senate committee heard testimony in Phoenix on border violence. Lieberman, an independent Democrat from Connecticut, and Sen. John McCain, a Republican on Lieberman's panel, told FOX News that the United States needs to step up the fight against the drug cartels. The two senators were in Arizona, McCain's home state, to hear from local officials on their advice for dealing with the drug-fueled violence many fear is spilling across the border.