More than a century passed between the impeachment of Andrew Johnson in 1868 and the almost-impeachment of Richard Nixon in 1974. Since then, the intervals have been getting shorter — a sort of Doppler effect. It was 24 years after Nixon’s resignation that President Bill Clinton’s case came before the House and only 21 years after that that the impeachment investigation of President Trump began.

Impeachment may soon become routine. The nation is at war with itself. If Hillary Clinton had been elected in 2016, Republicans might have tried to impeach her. Indeed, if impeachment becomes a regular tactic of the opposition, America will have informally adopted a quasi-parliamentary system of governance.

How would this serve the country? It would be a quantum leap in partisan antagonism. In the past, Americans regarded impeachment as an extreme rarity, a sort of civic apocalypse. In the future, it might become merely another ritual of hard-ball politics.

I can think offhand of at least a half-dozen presidents who might have been impeached but weren’t. Would Lincoln’s suspension of habeas corpus have been sufficient grounds? Could Woodrow Wilson have been impeached for ordering the racial segregation of workers in the Post Office and other federal departments? Franklin Roosevelt had a foxy way with the truth, and Republicans might have persuasively accused him of abuse of power in lying repeatedly as he maneuvered America toward involvement in World War II.

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