It was also meant to reduce the risk that impeachment would be a partisan matter, in which a president’s critics would seek to undo the results of elections and in which the president’s supporters would defend him no matter what. The framers’ goal was to discipline and constrain political debates.

Prominent among the category of high crimes and misdemeanors would be “a scheme of peculation or oppression” (a concern of James Madison, who was focusing on both economic self-dealing and violations of civil rights); interference with the democratic process in procuring the office “in the first instance” (Mason, who was concerned with corruption and bribery in connection with presidential elections); betrayal of “trust to foreign powers” (Madison again, who was concerned with disloyalty); and trampling “upon the rights of freemen” (an anonymous commentator in Massachusetts, writing under the name of Cassius, who was concerned with invasions of liberty).

In short, the constitutional standard was meant to capture egregious abuses of the public trust — in Alexander Hamilton’s words, offenses “of a nature which may with peculiar propriety be denominated POLITICAL, as they relate chiefly to injuries done immediately to society itself.”

In light of the historical background, we should be able to see why so many Democrats have been right to be cautious about impeachment proceedings against Mr. Trump. Untruthful tweeting, barbaric rhetoric, apparent indifference to climate change, a proposed citizenship question on the census, restrictions on entry into the United States by people from specified countries — none of these can easily be counted as a high crime and misdemeanor.

The constitutional background also helps explain the game-changing impact of President Trump’s conversation with Ukrainian President Volodymyr Zelensky. The facts are still emerging, but it is reasonable to worry that the president may have abused his authority in two different ways.

First, he appears to have pressed the leader of a foreign country to investigate a political rival — and thus to interfere with the democratic process in the United States. Second, he appears to have pressed that leader to commence a criminal investigation of two American citizens — and thus to intrude on civil liberty (assuming, as it appears, that the investigation would have been baseless). In the coming weeks, the House of Representatives will have to get clear on exactly what happened here, and also on whether other potential grounds for impeachment warrant serious consideration under the legal standard.

At age 78, Jefferson feared, “Our government is now taking so steady a course, as to shew by what road it will pass to destruction, to wit, by consolidation first; and then corruption, it’s necessary consequence.” Impeachment was meant to be the principal line of defense against that consequence.