View of the U.S.–Mexico border wall on January 7th, 2019 in Tijuana, Mexico. President Donald Trump is considering declaring a national emergency if Democrats do not approve of $5.7 billion in funding to build a wall. (Photo: Sandy Huffaker/Getty Images)

The United States has been in a near-constant state of emergency for 40 years. Now, President Donald Trump is considering treating the border as one.

On Sunday, Trump told reporters that he was considering invoking executive authority to resolve the government shutdown and secure funding for his border wall. "I may declare a national emergency dependent on what's going to happen over the next few days," Trump said, according to the Hill.

Immediately, politicians and experts from both sides weighed in, disavowing this statement and threatening legal action. "He'll face a challenge, I'm sure, if he oversteps what the law requires when it comes to his responsibility as commander-in-chief," Senator Dick Durbin (D-Illinois) said on CBS.

While experts say it's possible for the president to use some of his emergency powers to build a border wall, they also agree it would be an overstep—at least "a violation of constitutional norms," as the New York Times reports, sure to be settled in the courts. Reports show the president's claims about the "threat" of illegal immigration are unfounded, although the conditions for asylum seekers are worsening.

This is not the first time a president has contemplated such authority: According to the Brennan Center for Justice at New York University, a "vast set of laws gives the president greatly enhanced powers during emergencies." These include 136 statutory powers that touch on everything from the military to criminal law—and 96 require only the president's signature.

Here's how we got here.

The State of Emergency Emerges

Under the U.S. Constitution, presidents have amassed many powers that spring to life during crisis. President Harry Truman first declared a state of emergency during the Korean War, in an order that remained in effect until Congress attempted to regulate this authority years later, according to the Lawfare Institute. In 1976, Congress passed the National Emergencies Act, codifying—without truly restricting—this authority. The law gives a president the power to declare a national emergency when she or he wishes. Under the act, an emergency lapses after a year, unless it's renewed—and it often is.

President Jimmy Carter declared the first national emergency under the NEA in 1979, with an order blocking Iranian government property from entering the U.S. in response to the Iran hostage crisis. Carter determined that this situation, like the many to follow it, met the criteria of being "an unusual and extraordinary threat to the national security."

Although the act is intended to combat threats, it also authorizes far-reaching powers, which critics consider a threat of their own. The Brennan Center has catalogued many it considers easily exploitable, including the ability to suspend a ban on human testing of chemical and biological weapons, or a complete White House takeover of radio and wire communications. A president does not necessarily invoke all of these powers when declaring an emergency, nor are they all relevant or even possible. (The researchers note that one statute, still on the books, exempts World War II veterans from the draft.) However, as The Atlantic reports, Trump could still use the act for a "presidential power grab," giving him control over, say, Internet traffic and computer systems—including voter databases.

Four Decades of Emergencies

Since that first order in 1979, American presidents have declared 58 national emergencies. According to the Brennan Center's running count, 31 of these are still in effect—including the ban on Iranian property, which was extended in November of 2018. In other words, the country has been in some state of emergency for almost four decades.

These 58 national emergencies include declarations over dealings with Yemen, Syria, and North Korea, among others; sanctions against an array of terrorist groups, including one after 9/11; and various orders concerning nuclear weapons, diamonds imported from Sierra Leone, and the 2009 swine flu epidemic. Most recently, George W. Bush declared 13 and Barack Obama 12, most of which are still in effect, according to CNN.

Trump's States of Emergency

So far, the president has declared three national emergencies under the National Emergencies Act, according to the Brennan Center. The first was in December of 2017, when Trump sanctioned 13 people for human rights abuses and corruption using an executive order. Many were generals and heads of state accused of ordering executions and mass murder, including ethnic cleansing of the Rohingya Muslim minority in Myanmar.

The second came in September of 2018. Criticized as too broad at the time, the order sanctioned people found to be involved in hacking and social media campaigns for the purpose of influencing elections, Politico reports. In November, Trump declared a third national emergency over Nicaraguan President Daniel Ortega's regime and its "use of indiscriminate violence and repressive tactics against civilians."

The opioid crisis gets an honorable mention; although Trump said he would declare a national emergency over the crisis, the White House designated it a public-health emergency instead. However, a year later, Pacific Standard found that officials squandered their legal powers under the declaration.

Now, the president is contemplating a national emergency that few are calling for. But as with the opioid crisis, the president's statement may never become a declaration. "We can call a national emergency because of the security of our country, absolutely," he said on Friday. Then: "We can do it. I haven't done it. I may do it."

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