The timing of this is spoopy, to say the least. If it had made it through the barrier (or cheese slice as my motorcycling frens like to call those things) it would have coincided with the lead vehicle. The argument against this being an attempt is that it would likely have not penetrated the presidential limo, but it could have been a statement, an attempt to stop the motorcade for further action (check the woods right nearby), or as some suggest, remote controlled.