President Trump declared a national emergency to free up funds to build a wall without congressional approval on Friday, adding that other presidents have called national emergencies on other topics "many times before." The National Emergencies Act of 1975 allows the president to declare a national emergency, but he must outline the specific emergency powers he is using under existing statutes.

According to the Brennan Center, there have been 58 national emergencies called by presidents since 1979. Thirty-one of those national emergencies are still in effect.

Here is a list of when national emergencies have been used, and what their purpose was:

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President Jimmy Carter

Nov. 14, 1979 (still in effect): A national emergency in response to the Iran hostage crisis, which froze Iran's assets in the United States;



A national emergency in response to the Iran hostage crisis, which froze Iran's assets in the United States; April 17, 1980: Further Prohibitions on Transactions with Iran, never terminated or continued.



President Ronald Reagan

Oct. 14, 1983: Continuation of Export Control Regulations, revoked in 1983;



Continuation of Export Control Regulations, revoked in 1983; March 30, 1984: Continuation of Export Control Regulations, revoked in 1985;



Continuation of Export Control Regulations, revoked in 1985; May 1, 1985: Prohibiting Trade and Certain Other Transactions Involving Nicaragua, revoked in 1990;



Prohibiting Trade and Certain Other Transactions Involving Nicaragua, revoked in 1990; Sept. 9, 1985: Prohibiting Trade and Certain Other Transactions Involving South Africa (in response to apartheid), revoked 1991;



Prohibiting Trade and Certain Other Transactions Involving South Africa (in response to apartheid), revoked 1991; Jan. 17, 1986: Prohibiting Trade and Certain Transactions Involving Libya, revoked 2004;



Prohibiting Trade and Certain Transactions Involving Libya, revoked 2004; April 8, 1988: Prohibiting Certain Transactions with Respect to Panama, revoked 1990.



President George H.W. Bush

August 2, 1990: Blocking Iraqi Government Property and Prohibiting Transactions with Iraq, revoked 2004;



Blocking Iraqi Government Property and Prohibiting Transactions with Iraq, revoked 2004; Sept. 30, 1990: Continuation of Export Control Regulations, revoked 1993;



Continuation of Export Control Regulations, revoked 1993; Nov. 16, 1990: Chemical and Biological Weapons Proliferation, revoked 1994;



Chemical and Biological Weapons Proliferation, revoked 1994; Oct. 4, 1991: Prohibiting Certain Transactions with Respect to Haiti, revoked 1994;



Prohibiting Certain Transactions with Respect to Haiti, revoked 1994; May 30, 1992: Blocking "Yugoslav Government" Property and Property of the Governments of Serbia and Montenegro, revoked 2003.



President Bill Clinton

Sept. 26, 1993: Prohibiting Certain Transactions Involving UNITA (a political party in Angola), revoked 2003;



Prohibiting Certain Transactions Involving UNITA (a political party in Angola), revoked 2003; Sept. 30, 1993: Measures to Restrict the Participation by United States Persons in Weapons Proliferation Activities, revoked 1994;



Measures to Restrict the Participation by United States Persons in Weapons Proliferation Activities, revoked 1994; June 30, 1994: Continuation of Export Control Regulations, revoked 1994;



Continuation of Export Control Regulations, revoked 1994; Aug. 19, 1994: Continuation of Export Control Regulations, revoked 2001;



Continuation of Export Control Regulations, revoked 2001; Sept. 29, 1994: Measures to Restrict the Participation by United States Persons in Weapons Proliferation Activities, revoked 1994;



Measures to Restrict the Participation by United States Persons in Weapons Proliferation Activities, revoked 1994; Oct. 25, 1994: Blocking Property and Additional Measures With Respect to the Bosnian Serb- Controlled Areas of the Republic of Bosnia and Herzegovina, revoked 2003;



Blocking Property and Additional Measures With Respect to the Bosnian Serb- Controlled Areas of the Republic of Bosnia and Herzegovina, revoked 2003; Nov. 14, 1994 (still in effect): Proliferation of Weapons of Mass Destruction, continued in November 2018;



Proliferation of Weapons of Mass Destruction, continued in November 2018; Jan. 23, 1995 (still in effect): Prohibiting Transactions with Terrorists Who Threaten to Disrupt the Middle East Peace Process, continued in January 2018;



Prohibiting Transactions with Terrorists Who Threaten to Disrupt the Middle East Peace Process, continued in January 2018; March 15, 1995 (still in effect): Prohibiting Certain Transactions with Respect to the Development of Iranian Petroleum Resources, continued in March 2018 and expanded in August 2018;



Prohibiting Certain Transactions with Respect to the Development of Iranian Petroleum Resources, continued in March 2018 and expanded in August 2018; Oct. 21, 1995 (still in effect): Blocking Assets and Prohibiting Transactions with Significant Narcotics Traffickers, continued in October 2018;



Blocking Assets and Prohibiting Transactions with Significant Narcotics Traffickers, continued in October 2018; March 1, 1996 (still in effect): Regulation of the Anchorage and Movement of Vessels with Respect to Cuba, modified by President Obama in 2016 and again by President Trump in February 2018;



Regulation of the Anchorage and Movement of Vessels with Respect to Cuba, modified by President Obama in 2016 and again by President Trump in February 2018; May 22, 1997: Prohibiting New Investment in Burma, terminated in October 2016;



Prohibiting New Investment in Burma, terminated in October 2016; Nov. 3, 1997 (still in effect): Blocking Sudanese Government Property and Prohibiting Transactions with Sudan, continued in October 2018;



Blocking Sudanese Government Property and Prohibiting Transactions with Sudan, continued in October 2018; June 9, 1998: Blocking Property of the Governments of the Federal Republic of Yugoslavia (Serbia and Montenegro), the Republic of Serbia, and the Republic of Montenegro, and Prohibiting New Investment in the Republic of Serbia in Response to the Situation in Kosovo, revoked in 2003;



Blocking Property of the Governments of the Federal Republic of Yugoslavia (Serbia and Montenegro), the Republic of Serbia, and the Republic of Montenegro, and Prohibiting New Investment in the Republic of Serbia in Response to the Situation in Kosovo, revoked in 2003; July 4, 1999: Blocking Property and Prohibiting Transactions with the Taliban, revoked in 2002;



Blocking Property and Prohibiting Transactions with the Taliban, revoked in 2002; June 21, 2000: Blocking Property of the Government of the Russian Federation Relating to the Disposition of Highly Enriched Uranium Extracted from Nuclear Weapons, expired 2012;



Blocking Property of the Government of the Russian Federation Relating to the Disposition of Highly Enriched Uranium Extracted from Nuclear Weapons, expired 2012; Jan. 18, 2001: Blocking Property of the Government of the Russian Federation Relating to the Disposition of Highly Enriched Uranium Extracted from Nuclear Weapons, revoked in 2004.

President George W. Bush

June 26, 2001 (still in effect): Blocking Property of Persons Who Threaten International Stabilization Efforts in the Western Balkans, continued in June 2018;



Blocking Property of Persons Who Threaten International Stabilization Efforts in the Western Balkans, continued in June 2018; Aug. 17, 2001 (still in effect): Continuation of Export Control Regulations, continued August 2018;



Continuation of Export Control Regulations, continued August 2018; Sept. 14, 2001 (still in effect): Declaration of National Emergency by Reason of Certain Terrorist Attacks, continued in September 2018;



Declaration of National Emergency by Reason of Certain Terrorist Attacks, continued in September 2018; Sept. 23, 2001 (still in effect): Blocking Property and Prohibiting Transactions with Persons who Commit, Threaten to Commit, or Support Terrorism, continued in September 2017;



Blocking Property and Prohibiting Transactions with Persons who Commit, Threaten to Commit, or Support Terrorism, continued in September 2017; March 6, 2003 (still in effect): Blocking Property of Persons Undermining Democratic Processes or Institutions in Zimbabwe, continued in March 2018;



Blocking Property of Persons Undermining Democratic Processes or Institutions in Zimbabwe, continued in March 2018; May 22, 2003 (still in effect): Protecting the Development Fund for Iraq and Certain Other Property in Which Iraq has an Interest, continued in May 2018;



Protecting the Development Fund for Iraq and Certain Other Property in Which Iraq has an Interest, continued in May 2018; May 11, 2004 (still in effect): Blocking Property of Certain Persons and Prohibiting the Export of Certain Goods to Syria, continued in May 2018;



Blocking Property of Certain Persons and Prohibiting the Export of Certain Goods to Syria, continued in May 2018; July 22, 2004: Blocking Property of Certain Persons and Prohibiting the Importation of Certain Goods from Liberia, revoked in November 2015;



Blocking Property of Certain Persons and Prohibiting the Importation of Certain Goods from Liberia, revoked in November 2015; Feb. 7, 2006: Blocking Property of Certain Persons Contributing to the Conflict in Côte d'Ivoire, terminated in September 2016;



Blocking Property of Certain Persons Contributing to the Conflict in Côte d'Ivoire, terminated in September 2016; June 16, 2006 (still in effect): Blocking Property of Certain Persons Undermining Democratic Processes or Institutions in Belarus, continued in June 2018;



Blocking Property of Certain Persons Undermining Democratic Processes or Institutions in Belarus, continued in June 2018; Oct. 27, 2006 (still in effect): Blocking Property of Certain Persons Contributing to the Conflict in the Democratic Republic of the Congo, continued in October 2018;



Blocking Property of Certain Persons Contributing to the Conflict in the Democratic Republic of the Congo, continued in October 2018; Aug. 1, 2007 (still in effect): Blocking Property of Persons Undermining the Sovereignty of Lebanon or Its Democratic Processes and Institutions, continued in July 2018;



Blocking Property of Persons Undermining the Sovereignty of Lebanon or Its Democratic Processes and Institutions, continued in July 2018; June 26, 2008 (still in effect): Continuing Certain Restrictions With Respect to North Korea and North Korean Nationals, continued in October 2018.



President Barack Obama

Oct. 23, 2009: Declaration of a National Emergency With Respect to the 2009 H1N1 Influenza Pandemic, was never terminated or continued;

Declaration of a National Emergency With Respect to the 2009 H1N1 Influenza Pandemic, was never terminated or continued; April 12, 2010 (still in effect): Blocking Property of Certain Persons Contributing to the Conflict in Somalia, continued in 2018;

Blocking Property of Certain Persons Contributing to the Conflict in Somalia, continued in 2018; Feb. 25, 2011 (still in effect): Blocking Property and Prohibiting Certain Transactions Related to Libya, continued in February 2018;

Blocking Property and Prohibiting Certain Transactions Related to Libya, continued in February 2018; July 24, 2011 (still in effect): Blocking Property of Transnational Criminal Organizations, continued in July 2018;

Blocking Property of Transnational Criminal Organizations, continued in July 2018; May 16, 2012 (still in effect): Blocking Property of Persons Threatening the Peace, Security, or Stability of Yemen, continued in May 2012;

Blocking Property of Persons Threatening the Peace, Security, or Stability of Yemen, continued in May 2012; June 25, 2012: Blocking Property of the Government of the Russian Federation Relating to the Disposition of Highly Enriched Uranium Extracted from Nuclear Weapons, revoked in 2015;

Blocking Property of the Government of the Russian Federation Relating to the Disposition of Highly Enriched Uranium Extracted from Nuclear Weapons, revoked in 2015; March 6, 2014 (still in effect): Blocking Property of Certain Persons Contributing to the Situation in Ukraine, continued in March 2018;

Blocking Property of Certain Persons Contributing to the Situation in Ukraine, continued in March 2018; April 3, 2014 (still in effect): Blocking Property of Certain Persons With Respect to South Sudan, continued in March 2018;

Blocking Property of Certain Persons With Respect to South Sudan, continued in March 2018; May 12, 2014 (still in effect): Blocking Property of Certain Persons Contributing to the Conflict in the Central African Republic, continued in May 2018;

Blocking Property of Certain Persons Contributing to the Conflict in the Central African Republic, continued in May 2018; March 8, 2015 (still in effect): Blocking Property and Suspending Entry of Certain Persons Contributing to the Situation in Venezuela, continued in March 2018;

Blocking Property and Suspending Entry of Certain Persons Contributing to the Situation in Venezuela, continued in March 2018; April 1, 2015 (still in effect): Blocking the Property of Certain Persons Engaging in Significant Malicious Cyber-Enabled Activities, continued in March 2018;

Blocking the Property of Certain Persons Engaging in Significant Malicious Cyber-Enabled Activities, continued in March 2018; Nov. 22, 2015 (still in effect): Blocking Property of Certain Persons Contributing to the Situation in Burundi, continued in November 2018.

President Donald Trump