The cost to personal liberty, the flagrant unconstitutionality, and the chilling effect on US international relations and tourism aside, this is ALSO a bad idea because it will have zero effect on the real bad guys.
If you are a bad guy, why would you bring a phone loaded with contacts? Why would you provide a real, rather than a fake social media account? For a real bad guy, it is trivially easy to circumvent this new check. For the rest of us, it's a massive inconvenience, invasion of privacy, and an almost certain invitation to both systematic abuse and abuse by bad-apple agents.
(BTW, topic drift... I was quite surprised to see financial data disclosure requirements described as "new". Unlike the phone search and social media stuff, the financial data part is _not_ new. It's been a requirement for certain visa applicants for at least 40 years. It doesn't currently happen at the border, but rather at visa application time. Perhaps the reason it's listed as being new is because it now includes visa-waiver-program countries too?)