Bomboy is the editor-in-chief of the National Constitution Center.

In the current intense debate over the fiscal cliff, even President Obama and the Republicans agree that invoking the 14th Amendment as a debt-ceiling weapon is out of bounds. But that doesn’t mean it can’t be used as a nuclear tactic.

Quite simply, there is a school of thought that the President already has the power to ignore the ceiling on the national debt imposed by Congress.

Last year, the Democrats and Republicans locked horns on new legislation to raise the debt ceiling, which would enable the federal government to continue to borrow money to continue its operations.

The compromise gave us the current fiscal cliff scenario, where steep tax hikes and sharp spending cuts start in January 2013, triggering a likely recession, unless Congress can reach the deal they avoided last year.

The brainstorm behind the fiscal cliff was that it would be so nasty that Democrats and Republican would be forced to reach a bipartisan deal, or face political disaster. So they agreed to work together in a committee, which then spectacularly failed.

And another doomsday clock is ticking: the debt ceiling limit is expected to be reached again by February, even if the fiscal cliff is averted.

The debt ceiling is a critical point in the current fiscal cliff talks. Democrats want an agreement now that includes a new debt ceiling as part of the solution.

The Republicans seem reluctant to bargain that point.

“We do have some leverage with the debt ceiling increase, more than we do right now,” South Dakota Republican Senator John Thune told Fox News on Friday. “The debt ceiling at least requires Congress to take action.”

Or does it?

The argument over the 14th Amendment as a nuclear debt threat goes like this: Section IV says that “the validity of the public debt of the United States, authorized by law… shall not be questioned.”

Therefore, if you believe that the “public debt” can’t be questioned in any context, the debt ceiling itself is unconstitutional.

One of the more recent proponents of the 14th Amendment threat is former President Bill Clinton, who broached the idea in July 2011.

In an online interview with The National Memo, Clinton said Newt Gingrich’s Republican caucus first came up with the 14th Amendment idea during Clinton’s time as president, and Clinton’s team researched the constitutional implications.

Clinton said he would use the 14th Amendment “without hesitation, and force the courts to stop me.”

As recently as Thursday, Obama spokesman Jay Carney said the 14th Amendment was off the table as a negotiating ploy.

“This administration does not believe that the 14th Amendment gives the president the power to ignore the debt ceiling–period,” Carney said.

But that doesn’t mean other key Democrats agree with the president. On Friday, Senate Majority Whip Dick Durbin said the White House needed to consider the 14th Amendment as an option. “I don’t think they ought to rule it out,” he said.

Representative Peter Welch (D-Vermont) is spearheading a petition in Congress next week that asks President Obama to use the 14th Amendment. He told The Huffington Post that the president could be backed into a corner if the Republicans stand fast on steep spending cuts as the price for raising the national debt ceiling—and the 14th Amendment would be his only option.

So what would happen if Obama decided to just borrow more without congressional approval?

The original intent of the 14th Amendment was to address concerns related to the Civil War. It’s undecided if the “public debt” section of the amendment is applicable to current circumstances.

What makes it nuclear is the uncertainty of the events that would follow the constitutional bombshell. The Republicans in the House could move to impeach Obama, but his conviction in the Senate would be highly unlikely.

The court fight over the 14th Amendment option could be protracted and complicated. There were dozens of legal opinions last July when the idea was first made public.

But the bigger concern would be the reaction of global markets to a potential constitutional crisis over the United States’ national debt.

The 2011 budget debacle resulted in the first-ever downgrade of America’s debt.

Josh Marshall, the editor of Talking Points Memo, says that the potential financial price of a 14th Amendment move may be enough to keep it out of the fiscal cliff talks.

“You’d also now have what amounted to two classes of Treasuries—the good ones and ones with an asterisk next to them. And as soon as you have that, at least some of the fixedness and clarity of what a US Treasury obligation represents would be blurred,” he said.