It should come as no surprise that Donald Trump, the Republican nominee for president, is as ignorant about constitutional law as he is about every other matter pertinent to the nation’s highest office. The letter Trump’s lawyers sent to The Times on Wednesday — in which he threatened to sue the newspaper for publishing an article detailing two women’s allegations that Trump had groped or kissed them without consent — is extraordinary in its complete misunderstanding of both the facts and the law. Trump’s threat to sue may be an empty one, as so many of his previous threats — intended mainly to energize his angry base — have been. But it is yet another frightening reminder of what a Trump presidency could bring.