Republicans on Wednesday were playing defense on Iran after blowback from an open letter to Tehran’s leadership signed by a majority of GOP senators.

One senator who signed the letter, John McCain (R-Ariz.), publicly admitted the letter may not have been the best way for Republicans to express their opposition to nuclear negotiations.

{mosads}“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 Tuesday night 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” is reached, McCain added.

Sen. Tom Cotton (R-Ark.) wrote an op-ed in USA Today to explain why he helped organized the letter, which 47 GOP senators signed. The open letter warns Iranian leaders that Congress or a future president could rip up a nuclear pact after President Obama leaves office. 

Cotton cast the letter as a response to Obama’s decision to skirt Congress in negotiating with Iran.

“That is why this week, I, along with 46 of my fellow senators, wrote Iranian leaders to inform them of the role Congress plays in approving their agreement. Our goal is simple: to stop Iran from obtaining a nuclear weapon,” Cotton wrote. 

Talk of the letter has dominated the halls of Capitol Hill and cable news shows, with critics arguing the GOP may have undermined their own efforts to block a nuclear deal with Iran. 

For the third consecutive day, the White House ripped the letter. Press secretary Josh Earnest called it an attempt to “sandbag” Obama during nuclear talks and leave only a military option on the table to deal with Iran’s nuclear program.

“It does come at an inappropriate time,” Earnest said. “And attempting to sandbag the president of the United States in the midst of negotiations he is engaged in, not just with Iran but with our international partners, is not just unprecedented but inappropriate,”

Earnest said “it’s just not true” that Congress has been cut out of the negotiations, saying that senior administration officials have kept select lawmakers updated on the talks. 

Secretary of State John Kerry called the letter “irresponsible” and flat wrong during a Senate hearing on Wednesday. 

And former Secretary of State Hillary Clinton in a message on Twitter ripped potential GOP candidates for president for signing the letter. 

GOP letter to Iranian clerics undermines American leadership. No one considering running for commander-in-chief should be signing on.

— Hillary Clinton (@HillaryClinton) March 11, 2015

Earnest also singled out a statement from an anonymous Republican Senate aide who told The Daily Beast that the White House has “no sense of humor” in handling criticism of its Iran strategy. 

“It’s not a laughing matter,” Earnest said.