It would appear that the ability to regulate interstate commerce gives the feds plenty of authority to create and operate the TSA.
TSA is merely a means of implementing that clearly granted power.
I was under the impression we were trying to shrink the involvement of the Federal government. The interstate commerce clause was originally intended to clear up regulations and taxes that some states had imposed on goods from other states under the Articles of Confederation. The idea was to free up trade, not place barriers to it, and, as someone else pointed out, travel is not commerce.