First, it strains credulity that this is in fact a national emergency given the President's waffling over declaring said emergency for months. If it were a true emergency he wouldn't have waited to see what happens before doing something. This is a power grab, plain and simple. Second, it is unconstitutional in that Congress, a coequal branch of government, has the power of the purse. Congress will have, upon passage of the bill to avert another shutdown, appropriated over $1 billion for border fencing. The President cannot bypass the will of Congress just because he didn't get as much money as he wanted.