As the saying goes, you don’t miss the water until the well runs dry: This deeply aberrant presidency threatens to cost the nation much more than even some of President Trump’s harshest critics may realize.

From 1988 to 1992, I was The Post’s correspondent in Buenos Aires, covering all of South America. It was a time when countries such as Argentina, Brazil, Peru and Chile — emerging from years of authoritarian rule — were struggling to reestablish democratic norms, and I learned one important lesson: It’s easy to lose the habits and values of democracy, but incredibly hard to get them back.

Perhaps most difficult is to recover lost faith in the rule of law. That is why Trump’s very public desire to use the legal system as a weapon against his political opponents is so damaging. “Lock her up” is more than a call to imprison Hillary Clinton. It is, potentially, a tragic epitaph for the consensus view of our legal system as a disinterested finder of fact and dispenser of justice.