Someone was able to pull it off quite successfully after 9/11. There are still people who believe that the terrorists who carried out the attacks came across the border from Canada. As Trump has fully well exploited already, all it takes is the germ of a half-truth or a full out lie and then let the conspiracists run with it. It's pretty much how he ran his campaign and certainly how he's running his government. We are in a pots-truth world.