It's bigger than the TSA -- it's about the entire DHS. Of the 23 agencies that were merged into the DHS, the TSA was the only one that didn't exist, except for a few functions contained in the former FAA Office of Civil Aviation Security. Unlike Customs, Border Patrol, FEMA, etc, the TSA had no existing infrastructure or culture. So, in some sense, the DHS IS the TSA.
In theory, you would have to disband the entire DHS and send the staff functions of the TSA back to the FAA. Congress would never let that happen because the TSA has become an economic boost to lots of industries and has become a non-trivial government employer in some pretty backwoods areas. One could probably make a case that contractor screeners would be cheaper, but, the DHS isn't about saving money.
Finally, the government (executive and legislative branches combined) are basically risk-avoiders. They would have to take a risk to disband the TSA, so, it won't happen.