The dangers of it.
I’m as unhappy about it as I am with all the other “national emergencies” that have been declared by other presidents (many of which are still in effect). I notice, though, that (as usual), many people are only about things that all presidents do when Trump does them.
As for why the next D president couldn’t do that, I fully expect (s)he will (and would regardless of the faux “precedent” that Trump is supposedly setting). The only legal way to rein in a president (as opposed to what Obama’s Justice Department was illegally doing to Trump prior to the election, in what the guy who was fired for lying to the FBI is now admitting was an attempted coup) is impeachment. It has been used far too seldom, which is why the president has accumulated too much power.
…constitutional structure aside, why is presidential unilateralism bad? Because our system was designed to make major shifts in government policy difficult, and that’s a good thing because it lowers the stakes of politics. We had experience in 1861 with what happens when a significant part of the country believes that the national government has become arrayed against it, and it’s not an experience we should want to repeat on any scale.
But the Left seems determined to do that, even though we have the guns.