The GOP letter sent to Iran could not have undermined Obama"plan because the plan was undermined by Obama himself. Essentially Obama was holding Iran to its demand. But that is not the issue

Obama's tactics over these six years have shown that he can't be trusted, that he is a horrible negotiator and that he has refused from day one to work within the US Constitutions of separate but equal powers. the presidents job is to execute faithfully the policies created by the legislative branch with disputes between resolved by the judicial.

Obama has ignored Congress from day one and has gotten very use to governing by fiat and in doing so this country is in a serious mess.

I am saddened that 47 GOP senators felt the need to write a letter to the Iranians but keep in mind that the Iran deal so badly thought out that despite desperate attempts to hear them out Obama proceeded in his usual arrogant way. so while I am sorrowful that the need was created I understand why the need was exercised.