"I believe that Buchanan's people were afraid that if Charleston and South Carolina were to be "let go", the first thing they would do would to make trade treaties with Europe. This would threaten a collision between the North and those countries in Europe who would come to South Carolina's aid to protect access to South Carolina's products. There was much talk of making Charleston a "port of entry" to Europe."
I am assuming that when you say "Let Go" you are meaning that South Carolina being allowed to seceed peacefully without warfare. It would seem that you are contridicting yourself between your reply to me and your reply to George. It seems to me that your are suggesting that there was indeed an implied possibility of a trade war threat (and therefore a loss of Revenue to other ports of entry) should South Carolina be, as you say, "Let Go". It is a matter of conjucture as to the extent of Revenue that would be losted, But it would still be a loss if what you say about trade treaties is correct.