This idea is still being considered, but there are serious questions being raised by security professionals. A news article I read (on MSNBC website?) earlier this year, with an interview by a security professional noted some possible serious problems with this proposal. The most critical one included that 'clean' US citizens whom supported a cause could qualify for a TT
Cards and then after a few flights on their own, setting up a situation where would be sure of not being subject to extra checks on future flights, then several would board a given flight or several groups of several given flights, sneaking in equipment or a bomb (in ways we won't discuss here) to do a act of terror. There is also the idea of those above high scrutinty like all of the great most of us is discriminatory and against our ideas.