So what you're saying is if congress won't give the president what he wants, he claims he needs it to protect America so then it's his responsibility to declare a national emergency and just take it. I'm sure the next democrat president is going just love this.
Illegal immigration is a MASSIVE problem for the U.S. American citizens are victimized in terms of crime and higher taxes and medical care as a direct result of many millions of illegals in America. These are undeniable facts. What's also clear is that he U.S. Congress has abdicated its responsibility to protect Americans and to protect our nation's immigration laws. Therefore, Trump is wholly within his right, and responsibility, to declare the emergency.
By the way, Obama also avoided obtaining congressional approval for his horrific deal with Iran, the Paris Accord, etc. Trump taking unilateral action is not unprecedented, as evidenced by the community organizer that preceded him. At least in Trump's case, he is working for the interests of the American people, as opposed to the detriment of the American people, as Obama habitually did.