In 1861, President Lincoln confronted a section of the body politic that refused to accept his election.  Instead of hunkering down and resorting to the ballot the next time around, they simply repudiated the entire electoral process and voted (with their feet and arms) for negation of the election results.  Lincoln responded on July 4: 

"Our popular government has often been called an experiment. Two points in it our people have already settled – the successful establishing and the successful administering of it. 

"One still remains – its successful maintenance against a formidable internal attempt to overthrow it.

"It is now for them to demonstrate to the world that those who can fairly carry an election can also suppress a rebellion; that ballots are the rightful and peaceful successors of bullets; and that when ballots have fairly and constitutionally decided, there can be no successful appeal back to bullets; that there can no be no successful appeal except to ballots themselves, at succeeding elections.

"Such will be a great lesson of peace; teaching men that what they cannot take by an election neither can they take by a war; teaching all the folly of being the beginners of a war."

–July 4, 1861: Address to Congress

No president since Lincoln has faced the prospect of an internal rebellion as has Trump.  The departments of his own government are aligned against him.  The Justice Department in no way answers his summons.  The FBI uses overwhelming force to intimidate his supporters.  The intelligence agencies conspire for his removal.  The media, some of which appear to be merely part of the same apparatus, lie to the public in order to foment hysteria and create a popular clamor. 

"... a monstrous usurpation, a criminal wrong, and an act of national suicide."

–The Chicago Times, on the Emancipation Proclamation 

What is at stake, as in Lincoln's day, is not merely who is the occupant of the White House.  It is the survival of our democracy itself. 

The people voted for Trump in 2016.  Immediately, calls were heard for the Electoral College to be unfaithful to the electorate and select someone other than the winner.  There were cries that votes had been stolen (though the factual totals indicate that more fraudulent votes were cast for the opposition than for Trump). 

There were efforts to get the Cabinet to invoke the 25th Amendment.  Trump, like Lincoln, was lambasted as an incompetent who lowered the standards of the presidency by using tweets.

"His weak, wishy-washy, namby-pamby efforts, imbecile in matter, disgusting in manner, have made us the laughing stock of the whole world.  The European powers will despise us because we have no better material out of which to make a President[.] ... Take him from his vocation and he loses even these small characteristics and indulges in simple twaddle which would disgrace a well bred school boy."

–Salem Advocate, 1861

Like Lincoln, Trump was temperamentally unfit: 

"He is evidently a person of very inferior cast of character, wholly unequal to the crisis."

–Edward Everett in his diary

The reason for Trump's impeachment doesn't matter.  If he hadn't committed treason (based on a phony dossier – shades of the Dreyfus case and its phony bordereau), then he was guilty of accepting unlawful emoluments while in office (because people stayed at his hotels). 

Only the end result counted – that a duly elected president, chosen by the people, should not be allowed to hold office because one faction refused to accept the electoral result and was determined to replace him with a man (or woman) of its own choosing.

What's at stake in possible impeachment hearings, as well as the Mueller investigation, is no less than it was in Lincoln's day: do the people have the right to select their own government, or are their votes to count for nothing, and a faction, a gang, a cabal, or whatever name is given to it, be allowed a veto over the electorate to protect its own interests and purposes?

We are in a struggle no less significant than the Civil War, and testing the same principles, but the prize is worth the fight, if we can endure:

"[Once this is accomplished, America's] form of government is saved to the world; its beloved history, and cherished memories are vindicated; and its future fully assured, and rendered inconceivably grand.  To you, more than to any others, the privilege if given, to assure that happiness, and swell that grandeur, and to link your names therewith forever.

–Lincoln, Appeal to the border states, 1862