I’m afraid if we don’t make improvements in the system,” Mr. Turner said, “the public’s going to lose trust and confidence in that system and won’t pay any attention to it anymore.”
Seriously, why don’t they just put out press releases when there is a credible threat. Threats that aren’t realized, whether by their action, or the terrorists bad planning or whatever, are all going to contribute to the “crying wolf” syndrome. There’s no way around that, except a sucessful attack, and that would be–as we say in the trade–bad.
Not So Fast 
Problem is that with all the partisan bickering, they’d rather “cry wolf” than take the chance of not announcing a threat that comes through.