It is a myth that Mr. Trump seems to have fully bought into, given his defense of “beautiful” Confederate statues and monuments. Like Johnson, he uses derogatory language for people of color and he has expressed his preference for Nordic immigrants. Mr. Trump’s handpicked man in charge of immigration policy, the brain behind the separation of families in immigration detention camps, is Stephen Miller, who has recently been publicly revealed to be a white nationalist. The abolitionist feminist Frances Ellen Watkins Harper called Johnson an “incarnation of meanness,” words that are still applicable today.

Both Johnson’s and Mr. Trump’s concept of American nationalism is narrow, parochial and authoritarian. Johnson opposed the 14th Amendment, ratified in 1868, that guarantees equality before the law to all persons and citizenship to all born in the United States. Mr. Trump has threatened both to revoke its constitutional guarantee of national birthright citizenship and have the entire amendment overturned. Johnson’s highhanded actions and disregard of Congress led to Thomas Nast’s famous “King Andy” cartoon in Harper’s Weekly. Today Mr. Trump’s unaccountable style of governing reflects his Attorney General William Barr’s doctrine of unitary executive power, oblivious to the checks and balances and separation of powers in the Constitution.

The American republic was founded on the repudiation of the divine right of kings to rule. That is the reason that the impeachment clause of the Constitution holds elected officials, including the president, accountable for bribery and criminal wrongdoing.

Johnson and Mr. Trump not only managed to diminish their office but also engaged in actions that have dangerous repercussions for American democracy. Their crimes are not just specific impeachable acts but also the systematic undermining of the rule of law, democratic governance, human rights and the national interest. Johnson pardoned nearly all high-ranking Confederates who had taken up arms against the United States government. In one case, he also pardoned a white Virginian who murdered a black man in broad daylight and looked the other way at reports of massacres of freed people and harassment of Southern white unionists. Mr. Trump, against the advice of the Defense Department and the Navy, has just pardoned a Navy SEAL , Edward Gallagher, who violated the military’s rules of conduct. He has even hinted that he wants the disgraced Chief Gallagher at his rallies.

What Mr. Trump and his enablers call the “deep state” is nothing but the rules and norms of democratic government. It has become clear from the testimony of upstanding national security and foreign service officials like Ambassadors Marie Yovanovitch and William R. Taylor, Lt. Col. Alexander Vindman, Fiona Hill and David Holmes that he undermined the very fabric of the United States government in seeking to profit personally from the conduct of foreign policy, by withholding aid from a democratically elected anti-corruption Ukrainian government unless its officials investigated his domestic political rivals, the Bidens. Over 150 years ago, the testimony before Congress of ordinary patriotic Americans, former slaves, Southern unionists, Northern travelers to the post war South, Union Army officers and federal officials completely discredited Johnson’s racist policies.

Mr. Trump openly invites and, now we know, privately demands foreign interference in our elections, a scenario that the men who founded the American Republic and wrote its Constitution repeatedly warned against. He attacks his opponents and even supporters who do not agree with him on Twitter. Johnson, too, loved to vilify his opponents, like Frederick Douglass and Radical Republican congressmen. Both presidents precipitated a constitutional crisis that could be solved only through an impeachment process. The author Brenda Wineapple has written that Johnson was “the chief architect” of his own impeachment. The same is true of Mr. Trump.

Unlike with Nixon and Mr . Clinton, attempts to impeach Johnson and Mr. Trump preceded the actual impeachment inquiry because both systematically undermined federal laws and democratic institutions the moment they took office. Their personal narcissism and disregard for the principles of democratic governance led to early calls for impeachment. In Johnson’s case, violation of the Tenure of Office Act when he removed Lincoln’s Secretary of War, Edwin Stanton, led to his impeachment. While this law encroached on executive privilege, it was intended to prevent Johnson’s interference in congressional Reconstruction and his increasingly dangerous obstructionism. It was the law of the land when Johnson violated it by firing Stanton. Similarly, while it is certainly a president’s prerogative to appoint and fire American ambassadors, the removal of Ambassador Yovanovitch was the result of a sleazy attempt to pressure Ukraine’s government.