There aren't many government agencies or entities that are more popular with the American public that the United States Coast Guard. The Coast Guard has been rescuing us from violent seas and the aftermath of hurricanes since the early 1800's.
You can hardly find anyone with something negative to say about the coast Guard.
Until a September 11th.
Someone at the Coast Guard decided that they needed to conduct a very real sounding police action drill on the Potomac River in Washington. D. C., which they do frequently.
Except maybe on the anniversary of September 11th, and near the bridge where the president is traveling, at a time when he is very near the bridge, and when the news outlets weren't notified that radio traffic including the words "shots fired" was part of the drill.
Someone at CNN heard the radio traffic, went on the air nationwide with what they thought was a real interdiction by the Coast Guard and its armed boats, and essentially created a mini-panic.
Given the special circumstances of the day in question, the Coast Guard would have been better advised to move their drill to another day, and probably to make it clear to the media that what they might hear on radio scanners was not real.