Donald Trump’s criminal investigation into Representative Ilhan Omar—which is aimed at stripping her citizenship—is far more than just another attack on a vocal critic. As many have noted, this denaturalization push is an assault on the constitutional order itself. It amounts to a declaration of dictatorial or czar-like power, in which the sovereign can declare any foe an “enemy of the people” at will and delegitimize even the opposition’s duly elected representatives by fiat. All of which raises a question: Can Democrats do anything about this? Well, yes, they actually can. Senior House Democrats tell me they’re discussing a dramatic...