As far as I can tell, that's something the Trump admin has suggested would be a good idea, but isn't policy yet. However, they do conduct other electronic searches.
Then we get to debate what is constitutes as a social media acct? Any forum, any public comment board? Or what is more traditionally called social media, Reddit/Facebook/Instagram/Snapchat/Twitter and the like? Is email social media?
It's an impossible to comply with demand, that gives the person evaluating entirety to claim compliance or non-compliance based on whim. Not a far cry from a poll test.