I doubt Mr. Feller intended to imply the true Shakespearean meaning (Macbeth) of the phrase, but perhaps he did mean: taken down in a single evil stroke.
MACDUFF: [on hearing that his family and servants have all been killed]
All my pretty ones?
Did you say all? O hell-kite! All?
What, all my pretty chickens and their dam
At one fell swoop?
“At the speed of light, policies and political parties yield place to charismatic images” = McLuhan
Obama lost momentum and people were able to look beyond the fake smile. Obama is doing this speech to recharge the crisis and hit the accelerator. Obama needs more gasoline on the fire.