Fox News host Greta Van Susteren on Sunday blasted Republican senators for sending a "horrific" letter to Iran, and attempting an "end run" around the president.

David Remnick, editor of The New Yorker, told an ABC News panel that the 46 senators who joined Sen. Tom Cotton's (R-AR) letter undermine President Barack Obama's negotiations with Iran had made a "horrendous" mistake.

"If you read the text of the letter, it is the most condescending, infantile text assuming that the leaders of Iran -- whatever you may think of them, and there's a lot on the record to think terribly of them -- that somehow, that they have no idea what the American system is all about," Remnick explained. "It's an absurd comical exercise."

Susteren agreed: "I think that letter was horrific."

"It end runs the president, which I think is terrible," she said. "I think they could have achieved the same goal without sending a letter becoming pen pals with the leadership of Iran."

The Fox News host also condemned President Obama for trying to "end run the United States Senate and not calling this a treaty."