See other thread (why make up terrorist attack) --- create fears and the public is less against these typically unacceptable ideas. The Obama admin thought about this in 2011, almost put it into practice after a year of revision but ultimately decided no. These stuffs can have broad consequences and you can see how the last admin took their time and not rush into policy. On the surface, what's the big deal. Well, why wouldn't China and other authoritarian state want to do this? That is enough to said no. Considering that vetting has been successful to date, does this even help or will it be counter productive? U.S. Visitors May Have to Hand Over Social Media Passwords: DHS Former NSA lawyer says US border plans to demand tourists' browser history, phone data would be unlawful One former intelligence lawyer said the move would be 'tremendously intrusive' and could have a 'real cost' to effective intelligence gathering.
First they came for the Facebookers, but I have no Facebook so I said nothing. Then they came for the Twitterers, but I am not a Twit so I said nothing....