Trump’s threat to “close the border” is a desperate attempt to secure some kind of leverage over negotiating partners who show no signs of caving.
It is true that the president could shutter the U.S.-Mexico border by invoking his national security powers, and that this would inflict some economic pain on Democratic constituencies.
It is true that Trump has unilateral authority to initiate a thermonuclear armageddon, and that Nancy Pelosi would probably prefer to fund a border wall than perish in an atomic holocaust. But our president is the kind of demented nihilist who threatens to use his national security powers to inflict suffering on the American people, for the sake of narrow legislative gains!
That is enough to persuade congressional Republicans that they have no responsibility to remove a demented nihilist from the Oval Office.