Trump calling the crisis at the US southern border an "emergency" makes more sense than the last (10) that Obama declared (seen below). How is "blocking property" of someone called an "emergency"? The courts would need to consider these as not as important to the US as Trump's wall.
Here are the 28 active national emergencies - CNNPolitics
19. Blocking Property of Certain Persons Contributing to the Conflict in Somalia (Apr. 12, 2010)
20. Blocking Property and Prohibiting Certain Transactions Related to Libya (Feb. 25, 2011)
21. Blocking Property of Transnational Criminal Organizations (Jul. 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 (Mar. 6, 2014)
24. Blocking Property of Certain Persons With Respect to South Sudan (Apr. 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 (Mar. 9, 2015)
27. Blocking the Property of Certain Persons Engaging in Significant Malicious Cyber-Enabled Activities (Apr. 1, 2015)
28. Blocking Property of Certain Persons Contributing to the Situation in Burundi (Nov. 23, 2015)