I have long opposed the various efforts to impeach President Trump. Overturning an election should be a rare event, undertaken in only the most extreme circumstances. The process would create deep wounds in an already divided nation. And, as a practical matter, since it’s highly unlikely that a Republican-controlled Senate would vote by a two-thirds majority for conviction, the political effect could well be to vindicate Trump and aid his reelection.

But the events of the past few weeks have led me to support an impeachment inquiry. Trump’s efforts to pressure the new Ukrainian government, including his phone call with President Volodymyr Zelensky, were profoundly wrong. To direct U.S. foreign policy for personal political gain is the definition of abuse of power. Even many Trump defenders argue that what he did was undoubtably bad but claim that it does not rise to the level of an impeachable offense.

What has been far more troubling is Trump’s refusal to cooperate with the impeachment inquiry. Other presidents have contested a specific subpoena or request for documents. Trump is effectively rejecting Congress’s ability to hold him accountable. Even his staunch defender, the Wall Street Journal’s editorial page, conceded that Trump’s central argument, that the congressional inquiry is unconstitutional, is nonsense. “The House can organize impeachment more or less as it wants. . . . Like the president’s pardon power, the House’s impeachment power is among the least fettered in America’s founding charter.”

The rule of law has been built over centuries in the Western world, but it remains fragile because it is based on a bluff. The bluff is that, at the highest level, everyone will respect the rules, even though it might not always be possible to enforce compliance.

The rule at the heart of the U.S. system is the separation of powers. The Founders’ greatest fear was that too much power in the hands of government would mean the end of liberty. So they ensured that power was shared and that each branch would act as a check on the other. The crucial feature for James Madison , the chief architect of the Constitution, was “giving to those who administer each department, the necessary constitutional means, and personal motives, to resist encroachments of the others.” As he explained in Federalist 51: “Ambition must be made to counteract ambition.”

But the system only works if all sides respect it. Congress does not have an army or police force at its disposal. Nor does the Supreme Court. These institutions rely on the president to accept their authority and enforce their laws and rulings. When the Supreme Court held unanimously that President Richard M. Nixon could not use “executive privilege” to withhold the Watergate tapes, Nixon immediately agreed to comply, even though he knew it would mean the end of his presidency. More recently, in another place where rule of law is cherished, when Britain’s high court ruled that Prime Minister Boris Johnson’s prorogation of Parliament had been unlawful, he instantly said that although he disagreed, he would respect the ruling.

All modern U.S. presidents — both Republican and Democratic — have expanded their powers, and that expansion has been especially excessive in the past few decades. But Trump is on a different planet. He has refused to comply with wholly constitutional legislative requests for documents, information and testimony. He has diverted money toward a project clearly not funded by Congress, reportedly promised pardons for officials who might break the law, suggested that the military shoot migrants (which is unlawful) and now doubled down on his rejection of congressional oversight over him. Were Trump’s position to prevail, the U.S. president would become an elected dictator.

Democrats, meanwhile, are on firm constitutional ground but are being politically unwise. They should ensure that this impeachment inquiry looks and is fair. They should follow the precedents laid down during the last two impeachment investigations. Impeachment is a political process, which means that public support is vital. The American people may be more inclined to support impeachment after the Ukraine revelations, but they remain wary. The inquiry should be undertaken as a great act of public education, about the specifics on this case, but also about the U.S. system of checks and balances.

A democracy can turn into a tyranny not all at once, with a bang, but over time. Officials, often elected, often popular, can simply decide to weaken and then dispense with constitutional constraints or legislative checks. Liberty is eroded slowly but steadily. The Weimar Republic was a well-functioning liberal democracy that, within a few short years, using mostly legal processes, became a totalitarian dictatorship. Reflecting on that history, Yale’s Timothy Snyder wrote, “The conclusions for conservatives of today emerge clearly: Do not break the rules that hold a republic together, because one day you will need order.”

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