Presidential impeachments are vanishingly rare in American constitutional history: in the 230 years since ratification, only three presidents have faced serious attempts to remove them from office. And yet, as President Donald J. Trump’s tumultuous tenure continues, it seems increasingly plausible that we’ll see a fourth. In ordinary times, in ordinary presidencies, impeachment talk is considered taboo: the “I-word” is heard only on the political fringes, if it’s heard at all. Yet Trump’s first year in office saw four resolutions, containing a total of nine articles of impeachment against him, formally introduced in the House. Recent polls reveal strong support for an impeachment inquiry among the Democratic base. Should the Democrats recapture the House in the 2018 midterms, even reluctant members may find that pressure difficult to resist. The rancor engendered by our current impeachment debate bears out Alexander Hamilton’s prediction that impeachments would “seldom fail to agitate the passions of the whole community, and to divide it into parties.” But the scope of “high Crimes and Misdemeanors” shouldn’t turn on one’s opinion of any particular president. Partisans who lower the bar to impeachment in order to punish a president they revile — or raise it to save one they support — may, under future presidents, live to regret the standard they’ve set. This study touches on most of the specific charges directed against President Trump, but it does not answer the question of whether he should be impeached and removed from office. Instead, it is designed to serve as a primer on the purpose, history, and scope of the Constitution’s impeachment provisions — and a corrective to some of the popular myths that have grown up around the remedy. First among those myths is the notion that impeachment is reserved solely for criminal abuses of office. Perversely, as the power of the office has grown, that misconception has ensured that the federal official with the greatest capacity to do harm now enjoys stronger job protection than virtually any other American. But the remedy James Madison described as “indispensable … for defending the community against the incapacity, negligence, or perfidy of the Chief Magistrate” isn’t limited to violations of the law or abuses of official power. As the 1974 House Judiciary Committee report on “Constitutional Grounds for Presidential Impeachment” put it, impeachment was “intended to reach a broad variety of conduct by officers that is both serious and incompatible with the duties of the office.” “A good magistrate will not fear [impeachments],” Massachusetts’ Elbridge Gerry insisted at the Constitutional Convention, and “a bad one ought to be kept in fear of them.” Through the exercise of the “sole Power of Impeachment,” the House can call even the most powerful federal officer to account. That power should never be invoked lightly, but neither should Americans fear to wield it, should it become necessary.