To End a Presidency: The Power of Impeachment. By Laurence Tribe and Joshua Matz. Basic Books; 304 pages; $28.

FOR obvious reasons, interest in the process of impeaching an American president is soaring. But public understanding of what that would entail is not. The constitution calls for removal from office upon “Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors.” The House of Representatives has the “sole power” to determine whether there will be a trial in the Senate, where conviction requires a two-thirds majority. The House has voted to impeach two presidents—Andrew Johnson in 1868 and Bill Clinton in 1998. Richard Nixon averted impeachment by resigning. No president has ever been convicted. Johnson escaped in the Senate by a single vote; Mr Clinton was acquitted after 50 senators, all Republicans, voted against him.

In 1970 Gerald Ford, then a congressman, observed that “an impeachable offence is whatever a majority of the House” believes it to be. The unclear language of the constitution, the paucity of cases and the role played by partisan politics (unanticipated by the Founding Fathers) make Ford’s remark both plausible and unsatisfactory. A firmer definition is required. Laurence Tribe of Harvard Law School and his co-author Joshua Matz conclude that an impeachable act must involve corruption, betrayal or abuse of power, criminal or otherwise—an intentional evil deed that might inflict great injury on the nation.

In “To End a Presidency”, Mr Tribe and Mr Matz have written a powerful, clear and even-handed guide to the legal and political aspects of impeachment, which, as they point out, is “neither a magic wand nor a doomsday device”. Previous commentators have focused on the definition of an impeachable act, then assumed that justified suspicion of such conduct means a trial in the Senate. Mr Tribe and Mr Matz explain that the definition is but the “tip of the iceberg”. Other steps towards impeachment include public hearings on alleged misconduct; investigations; establishing a committee to consider a president’s removal; debates and votes by the committee and then the House; setting the rules for the Senate trial and conducting it; and voting by the senators on each charge. Just the investigative stage in the House inquiry into Nixon took ten months.

The authors emphasise that at every stage politicians have the discretion to nix the process. The constitution confers the power, not the duty, to proceed. They discuss the dangers to democracy of whichever course is chosen. Even a justified impeachment poses great risks, they note. Fans of the president (and in Donald Trump’s case, they would number tens of millions) are likely to regard the process as an illegitimate coup and might resist. If a putative impeachment effort were to fail, the country could be left “with a corrupt tyrant and his angry, vengeful supporters”.

“To End a Presidency” urges that “in assessing whether (and when) to impeach, we all must reckon with broader risks to the democratic system we’re trying to save.” Ultimately, the authors say, that calculation may sometimes “cut in favour of impeachment”. For all the acrimony of a trial and the possible backlash, allowing corruption or betrayal in the White House is “exceptionally risky” too.

Still, those ardently hoping for Mr Trump’s ousting, regarding him as irresponsible and impulsive, may not fully have considered the consequences. Would they really want to impose the enormous and extended pressure of an impeachment on such a man while he retains control over his vaunted nuclear button? Is the relatively brief benefit worth the jeopardy?

The question is academic: there seems to be no possibility that Mr Trump would be convicted by two-thirds of the Senate. That does not diminish the value of this enlightening book. It is the definitive treatment of a vital subject and will remain so long after this presidency.