U.S. government agencies under the current administration may demand access to your phone, laptop, or other devices when they question you. This is already happening to some of those passing through border checkpoints.
Though the Fourth Amendment should protect people from unreasonable search and seizure—such as requiring travelers to provide social media passwords and reveal their browsing history—what is considered “reasonable” is being decided by the officers on duty long before it reaches any courts of law. Rather than letting your travel be disrupted or allowing the government to copy off all the information on your devices (including not only social media and browsing history, but private communications by email or chat, private journals, your complete network of contacts, and any other data), it is advisable to take precautions before you travel. Sadly, this is particularly true for any person of color, with a name which sounds even vaguely Middle Eastern, who wears religious clothing such as a turban or hijab, or who has visible tattoos or piercings. Citizenship will not protect you from this kind of questioning.
Wired Magazine offers “A Guide to Getting Past Customs With Your Digital Privacy Intact“.
You should also review the ACLU’s page “Know Your Rights: What To Do When Encountering Law Enforcement at Airports and Other Ports of Entry Into the U.S.”
Journalists need to take extra precautions. They are both a targeted group and one with a greater need to protect the privacy of their data and the identities of their sources. The Committee to Protect Journalists has issued a safety advisory about crossing the U.S. border.