The president's national emergency declaration is of dubious legality. As a policy, it is worse than dubious.
First, the law. Although the president is commander-in-chief, the problem of border security is primarily a law enforcement problem, not a military problem. It is to be managed through civilian processes. Trump notes correctly that there are national emergency laws, but we must note that none has ever been used as is proposed by him. There is a justly famous Supreme Court precedent against what the president proposes. The law does not appear to be on his side.
Also worrisome is the mismatch between the policy and the problem. Drug traffickers, human traffickers, and potential criminals are crossing our border, but primarily at ports of entry, urban centers with existing security measures. They are not crossing out in the desert where the wall would be built. Furthermore, illegal border crossings have declined very substantially already. When a policy does not address its problem, there is a problem with the policy.
But the worst threat posed by this controversy is the threat to the remnants of principled political debate. When President Obama similarly stretched the limits of executive power, Democrats flocked sheepishly to support him, while Republicans howled and wrapped themselves in the holy mantle of constitutional fidelity. Now when it is Donald Trump, the two sides switch shamelessly, untroubled by their mutual hypocrisy. Shame seems to be in seriously short supply.
I'm Bob Evans, and that is my perspective.