I’ve thought about what’s the best thing to do with my phone when traveling. Getting a full contact, all access “welcome back to the USA” pat down makes you think about what else can happen 
Log out of Google, iCloud, etc, perhaps delete some apps. And if I have to carry a computer, it will be a chromebook.
1Password allows me to mark the info I may need as “Safe for Travel” then removes everything else and deletes the local vault. So if I am required to hand over my unlocked phone, there is a minimum of info to be inspected. And I’ve decided if security/police, etc. ever takes my phone out of my sight, it goes into the first trashcan I pass.
Unfortunately, the law already allows our phones to be searched when are within 100 miles of a border. Not just when we are crossing into or out of the country. So I expect this will just get worse.
…he has crossed the U.S. border hundreds of times
…he is speaking out, in part, to find out why he was flagged
Hm. Could be a relationship there 
How outmoded is this search at the border? As if people can’t use VPNs and the internet, or just ship an encrypted thumb drive. Sounds like more security theater.
In the mean time, a (alleged) Chinese spy talks her way into Mar-a-Lago.
The fact that they acquiesced after detaining him, making his future travel inconvenient, having his boss call, etc. tells me that he was within the law in refusing their search. Otherwise he would have been arrested.
n.b. not a lawyer 