Sen. John McCain (R-Ariz.), one of the signers of the controversial letter to Iran’s leadership, admitted Tuesday night that the letter might not have been the way to express frustration that President Obama isn’t working with Congress on nuclear negotiations with Tehran.

“What that letter did was tell the Iranians that whatever deal they make, the Congress of the United States will play a role,” he said on Fox News’s “On the Record with Greta van Susteren.”

“Maybe that wasn’t the best way to do that, but I think the Iranians should know that the Congress of the United States has to play a role in whether an agreement of this magnitude.”

Sen. Tom Cotton (R-Ark.) led the group of 47 GOP senators who signed the letter, which warned Iranian leadership that any deal that didn’t have congressional input could crumble in future years. A number of Democrats and foreign policy experts criticized it for trying to undermine the president.

President Obama, Vice President Biden, and former Secretary of State presumed presidential front-runner Hillary Clinton are among the high-profile Democrats who have publicly bashed the letter.

McCain blamed increasing partisanship for the conditions that spawned the letter. He pointed out the president’s unilateral action on immigration and normalizing the diplomatic relationship with Cuba as proof that the president has bucked working with Congress.

“It’s also symptomatic between the total lack of trust that exists now between we Republicans and the president,” he said.

“This has established a poisoned environment here which sometimes causes us to react maybe in not the most effective fashion.”