>>>You really need to think this through . . . if Congress has the ultimate authority, but that authority is governed by the 2/3 rule, which branch of government regulates commerce with foreign nations if a 2/3 vote fails?<<<
Using your logic ... if Congress has the ultimate authority, but that authority is governed by a majority rule, which branch of government regulates commerce with foreign nations if a majority vote fails?
I hate to do this to you, but below is roughly eighty pages of reading material on the subject. It's an 11th Circuit opinion that directly addresses your argument. It's notable for praising the lower court's decision (a rare event in legal circles), which also addresses your concern. I used to have a link to it, but no longer. It's available on the web, and recommended. Finally, I should add that the Supreme Court declined to hear the case. In other words, all three branches of government stand in opposition to your opinion, Judiciary, Legislative, and Executive.