If President Obama were to break the impasse with Republicans over raising the debt limit by taking unilateral action, such a move would have the potential to set off a firestorm of controversy and spark a protracted legal battle.

Top Senate Democrats say, go for it.

The White House has dismissed talk that Obama would rely on unusual measures to raise the nation's debt limit without Congress' approval, but administration officials also have warned that the country could default on its debt and trigger a new economic crisis if lawmakers don't increase the limit on borrowing.

Senate Majority Leader Harry Reid, D-Nev., is among those urging Obama to consider options like invoking the 14th Amendment to the Constitution to find ways around the $16.4 trillion legal cap on government borrowing. The amendment states that the "validity of the public debt of the United States ... shall not be questioned," which some lawmakers believe permits a way out of the debt limit jam.

The government hit the debt limit last month and is juggling the books to buy additional time for Congress to act. But those moves only buy a few weeks of wiggle room, which requires Congress to act -- likely by mid- to late-February -- to avoid a market-quaking default on U.S. obligations.

The White House has said emphatically that it does not believe that the 14th Amendment permits Obama to ignore the debt cap on U.S. borrowing, though it considered the question during the 2011 debt crisis.

"There is no Plan B. There is no backup plan," White House spokesman Jay Carney said Wednesday. "There is no alternative to Congress raising the debt ceiling."

A letter to Obama on Friday from Reid and Sens. Dick Durbin, D-Ill., Chuck Schumer, D-N.Y., and Patty Murray, D-Wash., doesn't mention the 14th Amendment, but aides to the senators said that's what they have in mind in urging the president to consider unilateral action.

"We believe you must be willing to take any lawful steps to ensure that America does not break its promises and trigger a global economic crisis -- without congressional approval, if necessary," the letter said.

Battling House and Senate leaders have made virtually no progress on a strategy for legislation to lift the debt cap. House Speaker John Boehner, R-Ohio, insists that any debt increase be matched by equivalent spending cuts. Obama, buoyed by his re-election victory, says he won't negotiate as he did in 2011, when he traded a $2.1 trillion debt increase for tight spending limits on agency budgets and automatic, across-the-board spending cuts if a congressional "supercommittee" failed to reach a budget agreement.

"Senate Democrats cannot ignore their responsibilities for political convenience -- and the American people will not tolerate an increase in the debt limit without spending cuts and reforms," said Boehner spokesman Michael Steel.

The impasse has people on both sides scratching their heads over how it will be resolved. The anxiety is such that some on the left are urging Obama to mint a coin worth perhaps $1 trillion to be deposited at the Federal Reserve and drawn upon to meet government obligations.