Declaration of national emergency is more common than we think. First of all it’s extraordinary situation which sharply increase power of The President. Regulated by National Emergency Act (1976).

On February 15 2019 new emergency declared by Mr Trump who surprised the world. But let’s take a look into history of emergency declaring (data from Wikipedia):

1. Totally declared 59 emergencies.
2. 32 emergencies currently on.
3. First one declared by President Wilson.
4. By President Roosevelt declared 4 (including emergency under threat from Nazi Germany).
5. President Truman declared 1 emergency (Korean War), President Nixon declared 2 emergencies.
6. President Carter declared emergency to block Iranian properties & prohibition of transactions.
7. President Reagan declared 6 emergencies for prohibiting trade and transactions with Nicaragua, South Africa, Libya, Panama.
8. President Clinton declared 9 emergencies for next reasons: prohibiting some transactions with Haiti, proliferation of weapons of mass destruction, prohibition of transactions with some individuals who disrupt Middle East peace process, prohibition of new investments in Burma, trade embargo against Sudan.
9. President Bush declared 13 emergencies: prohibition import of rough diamond from Sierra Leone, 9/11 terrorist attacks emergency, sanctions on Zimbabwe, sanctions on Syria, blocking selected individuals properties from Belarus, Congo, Lebanon, restrictions on North Korea because of the nuclear program.
10. President Obama declared 12 emergencies: blocking properties and prohibited some trades with Somalia, Libya, Yemen, Russian Federation, South Sudan, Central African Republic, Venezuela, Burundi.
11. President Trump declared 4 emergencies: certain sanctions on foreign interference in US election, sanctions due to Rohingya crisis in Myanmar, sanctions against selected Nicaragua officials, emergency to build the wall with Mexico.

As we can see from the list above President Trump declared 3 emergency before security wall funding emergency. Wall building was key point in election run and fulfilling of it may lead to re-election for second term. In priority to national emergency government shut down implemented to secure required funding. Government shut down did not give desirable result and leave President with no choice.