Transcript for GOP Letters to Iran Could Affect Unstable Negotiations
white house hitting back hard at republican senators who wrote directly to Iranian leaders warning them a nuclear deal would not last. ABC's Jon Karl is at the white house and, Jon, the president said these authorities are making common cause with Iranian hard-liners and the vice president went further and stopped just short of calling it treason. Reporter: He called it dangerous saying it's beneath the dignity of the congress to try to undermine the president as he conducts foreign policy. I spoke to one of the primary authors of the letter, he is defending it. Here's what he had to say. Isn't it the job of the president of the United States to negotiate with foreign governments. It's the presidejob to negotiate but us to approve. Reporter: You are going in and trying to insert yourself on negotiations between the president and a foreign government. We're simply trying to say that congress has a constitutional role to approve any deal, to make sure that Iran never gets a nuclear weapon. Reporter: The Iranians have also responded via Twitter of all things. The foreign minister saying, "It seems that the authors not only do not understand international law but are not fully cognizant of the nuances of their own constitution when it comes to the presidential powers in the conduct of foreign policy." So, George, the Iranians it seems leaks at this republican letter as basically the same way as the president does. One of the white house is concerned about if it fall as part the U.S. Could get more of the blame. Reporter: That's exactly right and you can believe that the white house will point the finger right at congress for undermining these talks if they do go down. Jon Karl, thanks very much. Now to the Boston marathon
This transcript has been automatically generated and may not be 100% accurate.