Some leading Republicans are demanding the head of Treasury Secretary Timothy Geithner following the unprecedented decision by credit agency Standard & Poor’s to downgrade the U.S. government’s long-term credit rating.

Jim DeMint, a GOP Senator from South Carolina, said President Barack Obama should “demand” Geithner’s resignation “and immediately replace him with someone who will help Washington [to] focus on balancing our budget and allowing the private sector to create jobs.”

DeMint added: “For months [Geithner] opposed all efforts to reduce the debt in return for a debt ceiling increase. His opposition to serious spending and debt reforms has been reckless and now the American people will pay the price.”

Republican presidential hopefuls congresswoman Michelle Bachmann of Minnesota and businessman Herman Cain have also called for Geithner to quit.

Similarly, Marsha Blackburn, a Republican congresswoman from Tennessee, told reporters that Obama “must get on board with Republican efforts to cut up the credit cards and put our economy back on the path to prosperity. The first step necessary in this process is for Treasury Secretary Tim Geithner to resign immediately. It’s time for new fiscal leadership in Washington.”

The downgrade comes just four months after Geithner told Fox News that there was no chance that US debt rating would be reduced, despite some warnings from S&P.

However, this past week, after Republican and Democrat lawmakers hammered out a debt ceiling deal, Geithner told ABC News he wasn’t certain if the package would lead to a downgrade from S&P or not. (The credit agency was hoping fort $4-trillion in cuts, rather than the $2,4-trillion envisioned by the government’s plan).

“It’s not my judgment to make and they have to make that judgment,” Geithner had said. “This is in some ways a judgment on the capacity of Congress to act and what this deal does is put us in a much better position to make those tough choices.”

This is not the first time Geithner has raised the ire of Republicans.

In 2009, under fire for his handling of the financial crisis, Geithner faced calls from some GOP members to quit. He also endured their wrath in connection with the huge bailout of AIG.

Ironically, Geithner has been maneuvering to resign anyway (long before the current debt downgrade imbroglio), but Obama and his top officials persuaded him to stay at least until the end of the president’s term.