On May 27th, I wrote here regarding the up & down shenanigans of the color-coded terror alerts:

I can propose at least three reasons for the very-public release of these warnings:

1) It's a very easy way for Ashcroft, the FBI, etc., to make Americans aware that they're doing something to prevent terrorism ("Wow, our tax dollar is being well spent.... they're working hard to protect us!")
2) If anything were to occur, it provides political cover (unlike 9/11, this time they could say, "Hey, it's not like we didn't warn you!")
3) With the election fast approaching, it's a well-known fact that the incumbent stands a much better chance of getting re-elected if the country is currently under some kind of threat of attack. In other words, fear favors the sitting president (and majority party, for that matter). Thus, Bush Inc. wants the country to constantly be reminded of imminent terrorist attacks and to remain "vigilant," keeping them in a steady-state of mildly paralyzing concern. Voters will then be too afraid to favor a change with regards to the highest office -- best to just "stay the course."

By most accounts, these warnings are simply a campaign tactic, nothing more, nothing less.

In Fahrenheit 9/11, one of the best running segments in the movie is interviews with Congressman/psychiatrist Jim McDermott, who agrees with my above sentiments stating that this administration is using fear to control the public by raising and lowering the colored "terrorist alert" with a politically-inspired agenda in mind. And again, this guy's insights mean something given he's a psychiatrist.