We're just going to simplify this subject matter to what the end result will be:
-No legal action will be taken against any of the Senators who signed the open letter.
-No measurable retaliation will be taken against any of the Senators during the next election cycle.
-The only thing of any measurable change is partisan political junkies will have their anger amplified for a few days before finding their next item to rage about.
The only reason to pay any attention to this story (unless you are directly involved in Middle-East affairs, that is), is if you enjoy being angry. All Republicans have stated is the already known fact that if they do not agree with the deal then it can be changed depending on who is elected President next. Have fun with your anger guys
Well, I do retract my earlier comment about what foreign leaders already expect or don't expect, and I was wrong, there was one who had to learn the hard way that deals are not permanent:
http://www.theguardian.com/world/2014/jun/22/poland-foreign-minister-alliance-us-worthless