"I'm embarrassed for them. For them to address a letter to the Ayatollah, who they claim is our mortal enemy, and their basic argument is 'don't deal with our president because you can't trust him to follow through on an agreement,'" Obama said in an interview with Vice News, "that's close to unprecedented."
Obama's comments were aired in a preview of the Vice interview.
His response follows some serious backlash the Republican senators received for sending the letter.
On Friday, Sen. Ron Johnson (R-WI), a member of the Senate Foreign Relations Committee who signed the letter, said he didn't regret the content of the letter but suggested sending it to Iranian leaders may not have been the best strategy.
Watch the clip of the Vice interview below: