Updated: 6:58 p.m.

Sen. Bernie Sanders (I-Vt.) and Rep. Peter DeFazio (D-Ore.) urged President Barack Obama on Wednesday to fire former Sen. Alan Simpson (R-Wyo.) as co-chairman of the White House deficit commission.

In a letter to Obama, the two liberals blasted Simpson for controversial comments he made in an e-mail to the executive director of the Older Women’s League, in which the Republican compared Social Security to “a milk cow with 310 million tits.”

Sanders and DeFazio said the remarks are “really quite beyond comprehension,” and the duo suggested Obama fire Simpson from his position as co-chairman of the commission, which is charged with providing Congress recommendations on how to trim the deficit.

“Co-Chairman Simpson’s comments are highly insulting to the tens of millions of senior citizens, persons with disabilities, widows and orphans who have contributed into this highly-successful program and who now utilize it,” the two wrote.

“Despite the many years of distinguished public service former Senator Simpson has dedicated to this country, his recent e-mail indicates that it is no longer appropriate for him to serve on the bi-partisan deficit reduction commission,” the letter said. “Therefore, in order for your commission’s recommendations to have credibility with Congress, we respectfully urge you to remove Senator Simpson from the commission.”

Rep. Raúl Grijalva (D-Ariz.), co-chairman of the Congressional Progressive Caucus, said Wednesday that Simpson should consider recusing himself from the commission if he “truly feels the disgust at Social Security he indicates in this letter.”

“It has become increasingly apparent that his disdain for Social Security is out of line with the majority of Americans,” Grijalva said in a statement. “His disregard for the integrity of the program, and for women in general, is unsettling. Americans have invested and earned their right to have a secure retirement, whether or not Sen. Simpson agrees.”

Simpson, who is known as a jokester on Capitol Hill, has drawn outrage from myriad interest groups since making his controversial comments in an e-mail Tuesday. Ashley Carson, executive director of the National Older Women’s League and the recipient of Simpson’s e-mail, launched a petition on her organization’s website calling for the one-time Senator’s ouster.

Simpson sent Carson an apology letter Wednesday, quipping, “Over the last 40 years, I have had my size 15 feet in my mouth a time or two.”