NEW YORK - President Barack Obama says he will not bypass Congress and cite an obscure part of the US Constitution to prevent a government debt default, but legal experts say it would prove difficult to challenge him in court should he change his mind.

Former President Bill Clinton argued last week that the 14th Amendment that states the "validity" of government debt "shall not be questioned" means that Obama could simply ignore the congressionally imposed debt ceiling and go on borrowing.

Obama has indicated he considered the possibility, but on Tuesday his spokesman, Jay Carney, appeared to rule it out.

"The Constitution makes clear that Congress has the authority, not the president, to borrow money and only Congress can increase the statutory debt ceiling. That is just a reality," Carney told reporters.

But if the country is about to go into default, the temptation to act to avert calamity will grow. Legal experts say if the president were tempted to act unilaterally he might escape without his actions being overturned in court.

Regardless of how controversial a 14th Amendment maneuver might be, a legal challenge would be very hard to mount and so far, no one has stepped forward to say they would challenge him in court.

Nor has anyone said they would sue him if he took the alternative, equally controversial, step of using his broad authorities as guardian of the constitutional order to unilaterally raise the borrowing threshold.

Theoretically, there are aggrieved parties who might consider legal action, including Congress, individual citizens or interest groups, and investors such as foreign governments.

Not unprecedented

A successful lawsuit against the executive branch of the United States would not be unprecedented.

In 1952, during the Korean War, the country's steel companies successfully sued President Harry Truman and prevented him from seizing mills in Ohio.

In 1971, The New York Times Company and the Washington Post Company took President Richard Nixon to court over the right to publish the Department of Defense's Pentagon Papers, detailing US involvement in Vietnam. The Supreme Court prevented Nixon from obtaining an injunction to block publication.

The plaintiffs in those cases were able to demonstrate standing, the legal doctrine under which parties must show they are harmed in order to bring a case in court. Anyone suing Obama over the debt ceiling would confront that same burden.

It wouldn't be enough for a plaintiff to claim that Obama is overstepping his authority or acting illegally. "In order to sue, you have to have injury in fact. The touchstone issue is, can someone get to court?" said Jonathan Zasloff, a law professor at the University of California, Los Angeles.

That same standard would apply if a party pre-emptively filed a lawsuit to stop Obama invoking the 14th Amendment.

Challengers might argue that relying on the 14th Amendment to raise the debt ceiling qualified as an abuse of executive power. But it would be extremely difficult for them to show that they would suffer specific harm such as lost money, property or rights, legal experts said.

The anti-tax group Club for Growth, which opposes increased federal borrowing, does not consider a legal challenge over the 14th Amendment likely, said executive director David Keating. "It's difficult to get standing," Keating said.

Individual members of Congress, congressional leaders, or Congress itself might have better luck suing, by claiming their constitutional authority to handle appropriations was violated by the President's move.

Take president to court

Members of Congress have taken presidents to court before.

In 1996, President Clinton signed the line-item veto act, allowing the president to veto separate parts of a spending bill. Six members of Congress who opposed the law sued the treasury secretary and the director of the Office of Management and Budget, claiming the law was an unconstitutional over-reach of executive power.

But in 1997 the Supreme Court said the lawmakers did not have standing to sue, ruling they did not allege personal injury or that the institution of Congress was harmed.

A third potential aggrieved party - the kind that typically shows up in court - is a jilted investor, whether an individual holding US treasury bonds or, perhaps, a foreign country that buys US government debt.

But if Obama were to raise the debt limit himself, he'd be paying bondholders back - the opposite of a government default. Instead of abrogating bond deals the President would be ensuring that obligations to creditors were met.

The best option for critics of an eventual 14th Amendment move by Obama may also be a longshot: Impeachment. Already one Republican House member, Representative Tim Scott of South Carolina, has said that if Obama bypasses Congress and raises borrowing on his own, it would be an "impeachable offense."