In case you hadn’t heard, President Trump joins the ranks of Presidents Johnson and Clinton as having been impeached by the House of Representatives. As the matter has progressed to the Senate for trial, his supporters have made any number of arguments in his defense, most of them in bad faith. The one that’s currently making my teeth itch, however, is the pseudo-legal argument that the Senate can only remove the President for a crime or “crime-like” behavior. Article II, §4 states:
The President, Vice President and all civil Officers of the United States, shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors.
The “conviction” in that passage refers to a proceeding under Article I, §3, Clause 6 which provides:
The Senate shall have the sole Power to try all Impeachments. When sitting for that Purpose, they shall be on Oath or Affirmation. When the President of the United States is tried, the Chief Justice shall preside: And no Person shall be convicted without the Concurrence of two thirds of the Members present.
So, treason and bribery are a subset of “high crimes and misdemeanors” but the Framers’ use of the word “other” indicates that there are more. When the Framers wrote the document, the phrase had a long history in parliament:
[A]t the time of the framing of the U.S. Constitution, the composite term “high Crimes and Misdemeanors” was a well-established, familiar legal term of art that the framers consciously borrowed from longstanding English practice and usage dating back four centuries. That meaning was not so much “vague” as simply broad: a sweeping delegation of power and responsibility to the legislative bodies entrusted with the impeachment power. The term “high Crimes and Misdemeanors” had a broad meaning in English practice and in the American understanding, confiding to the two houses of the national legislature (under the U.S. Constitution, the House and the Senate, exercising their respective roles in the impeachment process) a sweeping range of power to punish what those political bodies determined to be misconduct or abuse of power by executive and judicial officers of a wide variety of types.
The meaning of “high Crimes and Misdemeanors” was, so to speak, its own distinct thing. It was not a combination of “crimes” and “misdemeanors” as understood in today’s criminal-law sense. It was instead a unique legal term with its own meaning. The framers of the Constitution understood and used the phrase in that specialized sense, consciously adopting a known English-practice term of art in preference to other proposed formulations of the impeachment standard. And the ratification debates uniformly reflect that same broad understanding.
. . .
By the time the Constitutional Convention assembled in Philadelphia in 1787, the term “high Crimes and Misdemeanors” had been employed in the English practice of impeachment for more than four centuries. Historians, researchers, and constitutional scholars have plumbed the depths of English practice, discussing and debating the specifics of charges in impeachments dating back as early as 1386. For purposes of understanding the meaning of the U.S. Constitution, however, those details are perhaps less important than the broad observation that impeachment specifically for “high Crimes and Misdemeanors” – and frequently employing that very phrase – was a familiar political practice under the English constitution with a broad range of meaning marked by 400 years of experience and practice. 
Over the years, the English Parliament had developed and deployed the power of impeachment in its historic struggles to check the powers of the King and his ministers. The House of Commons had impeached and brought before the House of Lords for trial officers of the crown, including ministers and judges, that they believed had violated the constitution or laws; subverted the rights of Parliament or the system of government; abused or misused power; failed to perform the duties of office faithfully and competently; engaged in self-dealing behavior or misuse of funds; or were guilty of oppression, corruption, or other misbehavior or “mal-administration.”
Reflect on those categories for a moment. They describe a broad array of misconduct, not at all limited to criminality, as we today understand it. Not all persons impeached for the described offenses were convicted, of course. But the range of usage and practice – what was considered to lie within the scope of the power of impeachment for “high Crimes and Misdemeanors” – was unquestionably broad. That range plainly embraced “political” offenses: offenses against the constitution, laws, system of government, prerogatives of other institutions, or the rights and liberties of the people – as well as common law offences that might be punishable by ordinary criminal law.
. . .
As a matter of English practice and authoritative commentary by the mid eighteenth century, impeachment embraced offenses involving official misconduct not necessarily punishable by the ordinary criminal law.
That’s the legal backdrop. The practical effect is that “high crimes and misdemeanors” means whatever the Congress says it means. Impeachment and removal is a political process and was always meant to be. The Framers undoubtedly hoped that members of Congress would use sound judgment about what constitutes good government when making this determination and hoped that citizens would punish members of Congress soundly at the ballot box when they did not use such judgment; but ultimately there is no legal mechanism for gainsaying what Congress determines is a removable offense. Just don’t let Trump’s supporters confuse you with bafflegab about how removal isn’t Constitutionally permissible. If, as the House has charged, Trump withheld Congressionally approved financial aid to pressure Ukraine into meddling in our domestic elections for Trump’s benefit, such behavior falls squarely within the Constitutional definition of “high crime and misdemeanor.” If Senators don’t vote for removal, it’s not because the Constitution does not sanction the removal, it’s simply because they don’t want to.