Hypocrisy has become so commonplace among isolationist conservatives that it doesn’t always register, but this time it’s too blatant to ignore. ~Scott Paul

There are no real isolationists in Congress.  You certainly can’t find any of these people calling for withdrawal from Iraq or calling for an end to overseas intervention.  (The only people who might be reasonably described in some sense as “isolationist” are in the House, not the Senate.)  Opposition to the treaty does have to do with hostility to the United Nations.  There are Republicans making pro-sovereignty arguments, which come down to not wanting to accede to another international treaty.  In point of fact, the vast majority of the Republican caucus is robustly internationalist–they just don’t want the U.N. to have any say in what we do.  That may be many things, but it isn’t isolationist.