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(CNN) —  

If President Donald Trump moves to invoke a national emergency at the US border to bypass Congress and obtain funding to build his long-promised border wall, a battle in the courts over the questionable legality of spending those dollars would be virtually guaranteed.

But the United States is no stranger to national emergencies.

In fact, the US has been in a perpetual state of declared national emergency for four decades, and the country is currently under 31 concurrent states of emergency about a spectrum of international issues around the globe, according to a CNN review of documents from the Congressional Research Service and the Federal Register.

The federal government is now nearly three full weeks into a partial shutdown over funding for the President’s wall along the border with Mexico. The White House and Democrats in Congress are locked at an impasse: Trump is demanding nearly $6 billion, while House Democrats have vowed not to give him one dollar.

“I have the absolute right to declare a national emergency. I haven’t done it yet. I may do it. If this doesn’t work out, probably I will do it. I would almost say definitely,” Trump told reporters on Thursday morning, essentially vowing to bypass Congress if he can’t make a deal. “We have plenty of funds if there’s a national emergency.”

The National Emergencies Act of 1974 empowers the President to activate special powers during a crisis. Congress can undo a state of emergency declaration, but it would likely require a veto-proof majority, which is unlikely to come from the Republican-controlled Senate.

House Intelligence Committee chairman Adam Schiff told CNN’s Jake Tapper on “State of the Union” on Sunday that Trump doesn’t have the authority to declare an emergency. “If Harry Truman couldn’t nationalize the steel industry during wartime, this President doesn’t have the power to declare an emergency and build a multibillion-dollar wall on the border. So, that’s a nonstarter.”

But acting White House chief of staff Mick Mulvaney defended the possibility: “I’m actually heavily involved with it and have been working with all of the Cabinet secretaries to try and find money that we can legally use to defend the southern border,” he said on the same program. “Presidents have authority to defend the nation.”

The White House counsel’s office had begun laying the groundwork for a legal defense of the move on Thursday, according to officials familiar with the matter.

Not all national emergency declarations are so controversial. Trump has already issued three national emergency declarations during his tenure, most prominently a national emergency meant to punish foreign actors who interfere in American elections, though the move garnered bipartisan criticism for not going far enough. He’s also invoked emergency powers to slap sanctions on human rights abusers around the globe and on members of the Nicaraguan government amid corruption and violent protests there.

Here’s a full list of the 31 active national emergencies under the National Emergencies Act, dating back to the Carter administration:

1. Blocking Iranian Government Property (Nov. 14, 1979)

2. Proliferation of Weapons of Mass Destruction (Nov. 14, 1994)

3. Prohibiting Transactions with Terrorists Who Threaten to Disrupt the Middle East Peace Process (January 23, 1995)

4. Prohibiting Certain Transactions with Respect to the Development of Iranian Petroleum Resources (March 15, 1995)

5. Blocking Assets and Prohibiting Transactions with Significant Narcotics Traffickers (October 21, 1995)

6. Regulations of the Anchorage and Movement of Vessels with Respect to Cuba (March 1, 1996)

7. Blocking Sudanese Government Property and Prohibiting Transactions with Sudan (November 3, 1997)

8. Blocking Property of Persons Who Threaten International Stabilization Efforts in the Western Balkans (June 26, 2001)

9. Continuation of Export Control Regulations (August 17, 2001)

10. Declaration of National Emergency by Reason of Certain Terrorist Attacks (September 14, 2001)

11. Blocking Property and Prohibiting Transactions with Persons who Commit, Threaten to Commit, or Support Terrorism (September 23, 2001)

12. Blocking Property of Persons Undermining Democratic Processes or Institutions in Zimbabwe (March 6, 2003)

13. Protecting the Development Fund for Iraq and Certain Other Property in Which Iraq has an Interest (May 22, 2003)

14. Blocking Property of Certain Persons and Prohibiting the Export of Certain Goods to Syria (May 11, 2004)

15. Blocking Property of Certain Persons Undermining Democratic Processes or Institutions in Belarus (June 16, 2006)

16. Blocking Property of Certain Persons Contributing to the Conflict in the Democratic Republic of the Congo (October 27, 2006)

17. Blocking Property of Persons Undermining the Sovereignty of Lebanon or Its Democratic Processes and Institutions (August 1, 2007)

18. Continuing Certain Restrictions with Respect to North Korea and North Korean Nationals (June 26, 2008)

19. Blocking Property of Certain Persons Contributing to the Conflict in Somalia (April 12, 2010)

20. Blocking Property and Prohibiting Certain Transactions Related to Libya (February 25, 2011)

21. Blocking Property of Transnational Criminal Organizations (July 25, 2011)

22. Blocking Property of Persons Threatening the Peace, Security, or Stability of Yemen (May 16, 2012)

23. Blocking Property of Certain Persons Contributing to the Situation in Ukraine (March 6, 2014)

24. Blocking Property of Certain Persons With Respect to South Sudan (April 3, 2014)

25. Blocking Property of Certain Persons Contributing to the Conflict in the Central African Republic (May 12, 2014)

26. Blocking Property and Suspending Entry of Certain Persons Contributing to the Situation in Venezuela (March 9, 2015)

27. Blocking the Property of Certain Persons Engaging in Significant Malicious Cyber-Enabled Activities (April 1, 2015)

28. Blocking Property of Certain Persons Contributing to the Situation in Burundi (November 23, 2015)

29. Blocking the Property of Persons Involved in Serious Human Rights Abuse or Corruption (December 20, 2017)

30. Imposing Certain Sanctions in the Event of Foreign Interference in a United States Election (September 12, 2018)

31. Blocking Property of Certain Persons Contributing to the Situation in Nicaragua (November 27, 2018)

This story has been updated.

CNN’s Kevin Liptak contributed to this report.