In 2019, when Congress refused to pay for a wall on the Mexican border, then-President Donald Trump declared a national emergency and announced he would build the wall with money earmarked for other purposes. Democrats accused him of trampling on the Constitution’s separation of powers. The move “clearly…violates the Congress’s exclusive power of the purse,” House Speaker Nancy Pelosi (D., Calif.) declared. Some Republicans warned that a future Democratic president could use the same tactic to fund his or her own priorities.They were right. Last week President Biden declared that under a 2003 law, a national emergency—in this case Covid-19—empowers him to cancel student debt for up to 27 million people.