You are correct. The Constitution is very clear on States making treaties and dealing with international affairs with foreign Governments.
However, it is not unconstitutional to sell PUBLIC land held by the State when it is up for bid. I would expect a popular uprising by the citizens of Idaho and quite possibly the surrounding states via militia to revolt, arrest those public officials and foreign agents, and re institute a State Government.
This would be grounds for secession and even the impeachment of the President.
“This would be grounds for secession and even the impeachment of the President.”
Was Obama involved in this? I thought it was just the State of Idaho?