Let me guess. One week before July 4 the threat level will increase. On Sept 20, it will go down. On Nov 1, it will go up. On Jan 20, it will go down. And so on.....Well, we all have to remain vigilante, regardless. What makes me suspicious is this: either the authorities do not want to create "mass panic," or else the media is running away with this to make news. I'm always suspicious.
As you insinuated, if the threat is real, where is the elevated warning? Why no such warning? Yet, during every major holiday there IS one, regardless whether a specific plan was uncovered or not.
Believe me, I'm not questioning their commitment, but this particular decision seems unusual.