Good article that gives a historical perspective on Congressional involvement in foreign policy:
http://www.bloombergview.com/articles/2015-03-05/meddling-in-iran-talks-is-congress-s-job
http://www.bloombergview.com/articles/2015-03-05/meddling-in-iran-talks-is-congress-s-job
We can argue long and hard over the proper contours of the final deal with Tehran. But it’s wrong to suggest that Congress is misbehaving when it insists on protecting its prerogatives. Battles between the executive and legislative branches over foreign policy are as old as the republic. If the outcome of the current fight is a restriction on the freedom of this or a future president to go his own way, that’s a feature, not a bug.