The only thing I would add is that a political appointee is not in the job long enough, in most cases, to make a difference even if they wanted to change things. They are appointed to carry out the President's agenda -- 90% of which is budget-related. The appointee's job is to preserve what they already have and to work to get more. The 10% of the job might involve instituting the President's policies. But, this is almost always done within existing bureaucracies. As an example, despite all of the changes in the tax laws which occur every year, the IRS is still the same old IRS.

The real power and authority lies just beneath the surface with the top level of career SES management. Generally, they have been in their jobs for many years and define the organization's culture. An appointee who chooses to try to upset the apple cart is stonewalled and, if the careerist can get away with it, ignored. They understand that they will win the war of attrition because the appointee will be gone in a couple of years.

The DHS and TSA are what they are because of the Francines and the Gales and all of the other senior managers. The culture was, in fact, established by GW Bush when he told his cabinet right after 9/11 to make sure this didn't happen again on his watch. As a result, the agencies and senior officials that came together to form the TSA decided that the only way to ensure that another 9/11 didn't happen again on Bush's watch was to essentially establish martial law in the entire transportation sector.