Some of the less brain dead supporters are pointing to the fact that emergency powers aren't new, many presidents have used them including Obama. And that's true. No one is denying the authority exists. What makes this different is he's using an emergency in order to bypass the power of the purse which is specifically delegated to Congress as laid out in the Constitution (you know that thing you pretend to love). And, oh yeah, it's obviously not an emergency. That's why it's going to face serious challenges in court and a decent portion of republicans agree that it should.
Trump is just humiliated those snowfake democrats laid bare that he is a shit negotiator and has no idea what he's doing. The irony is by declaring an emergency he's just making it even more obvious.