This Secret Service Counter-Assault Team apparently has been around since at least the George W. Bush administration, by I admit I never noticed it.
Two days ago, the team's automatic weapons frightened protesters along President Obama's motorcade in Bristol, Virginia. I don't recall anyone previously reporting the team had pointed their assault weapons directly at crowds, but maybe there are more specific threats these days.
The shots fired on Kennedy, Ford and Reagan made something like this likely. Suicidal glory hogs like al Qaida even made it necessary. But maybe the Secret Service could keep their barrels a little higher or their tinted windows shut.