US Constitution: "The Congress shall have Power To... regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes;"
I do not see any element of that #CommerceClause that allows Congress to regulate what products the people buy, or from where.
It only allows for regulating trade with foreign nations.
But O.K. Let us assume that I am incorrect.
If Congress, in the case of Canada's prescription drugs and people of these united States of America; can Congress, the President, or even the Courts tell a united States American that they cannot buy products from ally nations with which they may freely travel?
Congress can put a ban on countries with which there is to be no trade whatsoever; thus limiting or prohibiting the purchase of any products from that country.
However, with relatively open borders between these united States and Canada, citizens may travel to Canada or Mexico in person and buy their prescription and freely bring them back into these united States of America.
When that same person buys products over the internet (prescription or others) it is the same as if that person traveled to that country (in 1785 terms) paid cash and came back home, transporting their personal property. #realDonaldTrump