The only real check on Trump’s power will come if he is punished in 2020 for these kind of illegitimate power grabs. Douthat seems to expect this. Chafetz and Kriner do as well. And it is true that if the wall is unpopular, declaring a state of emergency to do so is even more unpopular. If Trump loses reelection, then the weak man wins, and Trump becomes an object lesson in what not to do as president.
The thing is, he has a decent chance of winning. The economy is still strong, and this time he is running as the incumbent. Democrats will have plenty of opportunities to shoot themselves in the foot over the next 18 months, and if they don’t, Howard Schultz might shoot them instead. The 2016 election should have taught observers that it is possible for a man with low approval ratings to win. And if Trump is reelected, then all of this talk of weakness needs to be discarded.