Constitutional Grounds for Presidential Impeachment, Report by the Majority Staff of the House Committee on the Judiciary, Committee on the Judiciary, House of Representatives, One Hundred and Sixteenth Congress, First Session, December 2019 [open pdf - 733KB]
From the Introduction: "Impeachment is the Constitution's final answer to a President who mistakes himself for a monarch. Aware that power corrupts, our Framers built other guardrails against that error. The Constitution thus separates governmental powers, imposes an oath of faithful execution, prohibits profiting from office, and guarantees accountability through regular elections. But the Framers were not naïve. They knew, and feared, that someday a corrupt executive might claim he could do anything he wanted as President. Determined to protect our democracy, the Framers built a safety valve into the Constitution: A President can be removed from office if the House of Representatives approves articles of impeachment charging him with 'Treason, Bribery, or other high Crimes and Misdemeanors,' and if two-thirds of the Senate votes to find the President guilty of such misconduct after a trial."
U.S. House Committee on the Judiciary: https://judiciary.house.gov/