“Does the president have, as he says, ‘the absolute right’ to do this? Well, very little about presidential power is supposed to be absolute. But the [National Emergencies Act] can now be added to the list of statutes passed by Congress during its post-Watergate resurgence that were meant to rein in the presidency but have, in fact, empowered it.”
Washington Post

“The lawmakers of an earlier age… made an egregious oversight: They assumed that future presidents would use these extraordinary powers in good faith, to address genuine national emergencies. The Trump administration is a monument to their lack of foresight. In an unhappy syzygy, the areas where Congress has ceded the most power and the broadest discretion—immigration and national security—also happen to be Trump’s favorite playgrounds for both policy and politics.”
New Republic

“While the NEA provides broad authority to declare a national emergency, simply saying he thinks something is a national emergency does not provide Trump with authority to build a wall. In order to use emergency military construction authority, there must in fact exist a national emergency ‘that requires use of the armed forces.’ In other words, beyond declaring simply that a national emergency exists, the executive branch must be able to show that the emergency at issue necessitates use of the armed forces…

“There is no reasonable argument that families and children seeking asylum constitute an emergency that demands a military response… Trump’s proposal is the type of unilateral action one would expect to find in an authoritarian regime. The national emergency is not at our Southern border, it sits in the White House.”
Just Security

Minority view: “Everyone calm down about that declaration of National Emergency… the ominously vast grant of emergency authority boils down to Trump’s ability to shuffle around resources the Pentagon already has… [This is] a president exercising power delegated to him by a co-equal branch of government consistent with the structure of separation of powers—and likewise subject to review in litigation by another co-equal branch of government.”
Lawfare Blog

“Rather than continuing with a debate about whether or not to build a wall, Democrats should shift the debate to different ground: they should propose spending more money to ensure a smarter, more efficient and more humane border policy. Democrats have already supported this agenda in the existing budget, but by offering to spend more for these measures they can highlight the false choice that the administration is giving voters… Good border security does not mean building a big wall.”
CNN