[slg]

Isn't that incident evidence that the governments of the US, Spain, France, Portugal, and Italy all believed it was feasible that he could be smuggled out?

Also, the plane was only grounded because the flight plan took them through the airspace of US allies. If Snowden really was on the plane, they could have chosen a different route to avoid this issue. The US isn't going to shoot down a plane carrying a foreign head of state over international waters because they suspect a potential criminal is on board.