There should have never been a split. When the airlines were responsible for security it was an agreement between you and a private service. Just like Disney can demand to search your bag and deny you entry if you refuse. When the security was "federalized" it blew that argument out of the water. The fact that the TSA routinely turns passengers over to law enforcement when finding non-security related contraband pretty much shreds the administrative search dance around the 4th amendment.

As to the other argument about greater threat to aviation compared to other modes of transportation, isn't it amazing that thousands of GA and other charter flights have occurred every day since 9/11 without a single terrorist incident occurring due to un-screened passengers.