At actual border crossings, the practice at the time of the framers was not to carry along all of your private correspondence, business records, reading lists, and so forth. Related to that, given the complaints that started the war, I'd strongly expect that in Washington's day it was not permitted to perform unwarranted searches of one's sealed correspondence going through the US Post. [0]

As the ability to perform surveillance on members of the public expands, laws and regulations must be reconsidered with these new capabilities in mind if just outcomes are to be maintained. Laws, regulations, and punishments that were just and reasonable when one expected to learn about and prosecute one offender in -say- a million are likely unjust and unreasonable when one expects to learn about and prosecute every single offender. [2]

[0] See also Section 16 on numbered page 236 of [1]

[1] <https://govtrackus.s3.amazonaws.com/legislink/pdf/stat/1/STA...>

[2] Yes, there are offenses -such as murder- for which this doesn't hold. I'd expect that these are the minority of offenses.