The U.S. government has published its policy: they can take your laptop anywhere they want, for as long as they want, and share the information with anyone they want:
Federal agents may take a traveler’s laptop or other electronic device to an off-site location for an unspecified period of time without any suspicion of wrongdoing, as part of border search policies the Department of Homeland Security recently disclosed. Also, officials may share copies of the laptop’s contents with other agencies and private entities for language translation, data decryption, or other reasons, according to the policies, dated July 16 and issued by two DHS agencies, US Customs and Border Protection and US Immigration and Customs Enforcement.
You have to love that catchall line — makes other countries’ espionage practices look positively benign.
In even the medium term, it won’t work for the US to go it alone with this kind of policy. I wonder whether the next administration will be sane about border searches, or whether the rest of the world will devolve to our level of incipient police state. (The fact that it’s US citizens as well as furriners makes it harder for countries with working political systems to adopt the same level of arbitrary search, because their citizens will likely be more vigorous in objecting.)