In a joint letter that served as a warning to congressional Republicans, Senate Majority Leader Harry Reid, D-Nev., and his leadership team encouraged Obama to "take any lawful steps" to avoid default -- "without Congressional approval, if necessary."
The letter appeared to be an effort to push the White House to play hardball in its negotiations with Republicans as the federal government edges up against a legally imposed limit on borrowing.
Republicans have insisted that they will not increase the government's borrowing authority without deep spending cuts, including to entitlement programs. On Friday they rejected the idea of unilateral action by the president.
"The Democrat leadership hiding under their desks and hoping the President will find a way around the law on the nation's maxed-out credit card is not only the height of irresponsibility, but also a guarantee that our national debt crisis will only get worse," said Senate Minority Leader Mitch McConnell, R-Ky.
Michael Steel, a spokesman for House Speaker John Boehner, R-Ohio, said Americans "will not tolerate" increasing the debt ceiling without spending cuts.
Obama has said he considers raising the limit -- which the nation will hit in February -- an obligation of Congress because doing so allows the government to pay off debts it has already incurred.
Unlike in the summer of 2011, when Obama negotiated with Boehner in an effort to pair a debt-ceiling increase with a broad deficit-reduction package of spending cuts and new tax revenue, the president has insisted he will no longer negotiate spending concessions in exchange for a higher ceiling.
That has left both sides without a clear strategy for how to proceed in what is likely to be a bitter and protracted fight.
In their letter, Reid, Sen. Dick Durbin, D-Ill., Sen. Charles Schumer, D-N.Y., and Sen. Patty Murray, D-Wash., indicate that they will support Obama if he moves without Congress.
They wrote that the GOP position to block a debt-limit increase unless Democrats agree to cuts in Medicare and Social Security is "outrageous and absurd."
They urge Obama to act unilaterally "in the event that Republicans make good on their threat by failing to act, or by moving unilaterally to pass a debt limit extension only as part of unbalanced or unreasonable legislation."
One option some congressional Democrats have long advocated would involve Obama invoking the 14th Amendment to the Constitution to declare congressional action unnecessary for raising the limit.
The amendment holds that the validity of the country's public debt "shall not be questioned." Some constitutional experts believe that statement means that Congress cannot tie the government's hands to borrow funds to meet obligations the government has already incurred.
The White House has indicated that Obama does not believe the Constitution gives him the right to ignore the congressionally imposed limit on borrowing.
Officials have been less definitive, however, about another route: allowing the Treasury Department to mint a trillion-dollar platinum coin to bolster the nation's assets. The seemingly wacky idea has been gaining traction in recent days because of a law that allows the Treasury to mint coins of any value.
Asked recently about the coin, White House press secretary Jay Carney pointedly refused to rule it out as an option -- though he repeatedly indicated that there "is no Plan B" to congressional action.
In his statement, McConnell called the coin idea "ridiculous" and accused Democrats of considering "outright abdication of Congressional responsibility" in order to avoid cutting spending. The letter from Senate leaders came a week after a similar suggestion from House Minority Leader Nancy Pelosi, D-Calif. She said last week that if she were president, she would invoke the 14th Amendment to raise the debt ceiling "in a second."
"I've made my view very clear on that subject," she said. But, she added, "I'm not the president of the United States."
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