WASHINGTON – President Donald Trump set off a heated debate when he acknowledged he may declare a national emergency to free up funding for his proposed border wall, reopening a controversy that has its roots in the Revolution and has bedeviled many presidents since.

Though presidential emergencies often lead to bitter partisan disputes and occasionally wind up in court, they are relatively common. The United States is subject to more than 30 national emergencies, including one signed in 1979 by President Jimmy Carter days after the Iranian hostage crisis began.

"They’re declared for all kinds of things," said Kim Lane Scheppele, a professor at Princeton University's Center for Human Values. "They’re absolutely common, which is why nobody blinks an eye about the whole thing – and then you get a case like this."

Frustrated by opposition to his proposed wall on the U.S.-Mexican border, Trump said he is considering using a national emergency to bypass lawmakers. Experts said the president may be able to rely on several laws that would allow his administration to redirect military spending for the wall during an emergency.

The impasse over the border wall led to one of the longest government shutdowns in history.

Since 1976, when Congress passed the National Emergencies Act, presidents have declared at least 58 states of emergency – not counting disaster declarations for weather events, according to the nonpartisan Brennan Center for Justice. Dozens remain in effect, extended by subsequent presidents.

Most fall under the International Economic Emergency Powers Act, which allow a president to impose economic sanctions.

The use of emergency powers is older than the country itself. From 1775 to 1781, the Continental Congress approved a series of emergency acts dealing with the Revolutionary War, according to the nonpartisan Congressional Research Service.

The Militia Acts of 1792 gave President George Washington authority to take over state militias during the Whiskey Rebellion. In perhaps the best-known use of emergency powers from history, President Abraham Lincoln established a blockade on the ports of Southern states and suspended habeas corpus without congressional approval.

In modern times, presidents have used executive powers to impose sanctions, seize property and call up the National Guard.

In 2009, President Barack Obama declared a state of national emergency for the H1N1 swine flu pandemic. That emergency, which expired a year later, allowed for waivers of some Medicare and Medicaid regulations – for example, permitting hospitals to screen or treat an infectious illness off-site – and to waive medical privacy laws.

After the 9/11 terrorist attacks in 2001, President George W. Bush signed an order giving him broad powers. A subsequent executive order, signed in November of that year, activated the same law the White House may be considering – a provision that allows the president to redirect military construction money.

Experts said that authority has mostly been used overseas.

Elizabeth Goitein, co-director of the Brennan Center’s Liberty and National Security Program, said few would have disputed that a state of emergency existed after the 9/11 attacks. The president's emergency powers, she said, were conceived as a way to give the president the ability to act when Congress didn't have time to do so.

In the case of immigration or a border wall, Goitein said, Congress had plenty of time but chose not to act.

"This is a situation in which the powers are being used to get around the express will of Congress," she said. "That is particularly problematic."

Trump has signed three executive orders that relied in part on the National Emergencies Act, including an order in September that gave him power to slap sanctions on any foreign country that interferes in a U.S. election. That action was taken after criticism that Trump did not do enough to confront Russian meddling in the 2016 presidential election.

Experts said the idea of using a national emergency to build the president’s promised border wall would be novel, and some Democrats threatened to sue.

"We can call a national emergency and build it very quickly," Trump said last week. "But if we can do it through a negotiated process, we are giving that a shot."

Under the National Emergencies Act, the president must cite the specific emergency powers he is activating under statutes. According to the Congressional Research Service, there are hundreds of "provisions of federal law delegating to the executive extraordinary authority in time of national emergency."

Congress can terminate a declared emergency, but it requires a joint resolution – a high hurdle. Democrats in power at the House of Representatives would have to convince Republicans who control the Senate to join them in blocking Trump's move. Then they would have to get a signature from the president, the same person who declared the emergency in the first place, or override his veto.

The law requires Congress to “meet to consider a vote” on each emergency every six months. In 43 years of the National Emergencies Act, Congress has never done so.

Experts said Congress has given presidents considerable leeway by not providing a more thorough check on the use of national emergencies. Scheppele said she hopes the wall controversy refocuses the public's attention on the issue.

"I hope people say, 'Wow, what were we doing when we allowed the powers to come into effect in the first place?' "

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Contributing: Gregory Korte and William Cummings