"Evidence suggests that the Constitution’s framers believed that any offense deserving of impeachment would also violate established law. Article I, for example, provides that officials removed from office after an impeachment trial would also be liable to trial in the courts—a clarification that wouldn’t be necessary unless the impeachable conduct arises from breaking the law. Alexander Hamilton, in Federalist 65, explained that the Senate, rather than the Supreme Court, was the best venue for impeachment trials because, upon a successful conviction, it was likely that the removed official would then be subject to criminal trial in federal court “in the ordinary course of law.” It wouldn’t be proper, according to Hamilton, for the federal judiciary to preside over two trials of the same officer “for the same offense.”
An early test of the sort of vague charges at issue in the Trump case surfaced in the 1804 impeachment trial of Supreme Court Justice Samuel Chase, which arose from Jeffersonian opposition to the staunch Federalist. The House had voted to impeach Chase, essentially, for the “crime” of misapplying the law while sitting as a circuit court judge. Chase’s defense counsel, Luther Martin, a delegate at the Constitutional Convention, persuasively argued that impeachment must relate to acts “contrary to law.” In the end, six Jeffersonian Republicans crossed the aisle to acquit Chase."