The wonderful thing about Donald Trump's presidency (I never thought I'd begin a column this way), is that he brings us back to basics.
The basic difference between a democracy and a dictatorship comes down to means and ends.
Democracy is about means, not ends. If we all agreed on the ends (such as whether to build a wall along the Mexican border), there'd be no need for democracy.
But of course we don't agree, which is why the means by which we resolve our differences are so important. Those means include a Constitution, a system of government based on the rule of law, and an independent judiciary.
A dictatorship, by contrast, is only about ends. Those ends are the goals of the dictator — at a minimum, accumulating and preserving personal power. To achieve those ends, a dictator will use any means necessary.
Which brings us back to Mr. Trump.
The conventional criticism of Mr. Trump is that he is unfit to be president because he continuously breaks the norms of how a president should behave.
Mr. Trump's norm-breaking is unsettling, to be sure, but MR. Trump's more fundamental offense is that he continuously sacrifices means in order to build personal power.
He thereby violates a president's core responsibility to protect American democracy.
A president who shuts down government in order to get his way on a controversial issue, such as building a wall along the border with Mexico, and offering to reopen government as a concession when his opponents give in, is not protecting democracy.
He is treating the government of the United States as a bargaining chip. He is asserting power by any means possible. This is the method of a dictator.
A president who claims he has an absolute right to declare a national emergency and spend government funds that Congress has explicitly refused to appropriate for the ends he seeks is also assuming the role of a dictator.
A president who spouts lies during a prime-time national television address over what he terms an "undeniable crisis" at the southern U.S. border, which is in fact no crisis at all, is using whatever means are available to him to preserve and build his base of power.
The real international threat to America is not coming from Mexico. It is coming from a foreign government intent on undermining our democracy by propagating lies, turning Americans against each other and electing a puppet president.
We do not know yet whether Mr. Trump colluded with Vladimir Putin to win the 2016 election. What we do know so far is that Mr. Trump's aides and campaign manager worked with Mr. Putin's emissaries during the 2016 election, and that Putin sought to swing the election in favor of Trump.
We also know that since he was elected, Mr. Trump has done little or nothing to stop Mr. Putin from continuing to try to undermine our democracy. To the contrary, Mr. Trump has obstructed inquiries into Russian meddling.
The overall pattern is clear to anyone who cares to see it. Mr. Trump's entire presidency to date has sacrificed the means of democracy to the end of his personal power.
He has lied about the results of votes and established a commission to investigate bogus claims of fraudulent voting. He has attacked judges who have ruled against him with the goal of stirring up the public against them.
He has encouraged followers to believe that his opponent in the 2016 election should be imprisoned. He has condemned as "enemies of the people" journalists who report unfavorably about him, in an effort to fuel public resentment -- perhaps even violence -- against them.
To argue, as some Trump apologists do, that whatever Mr. Trump does is justified because voters put Mr. Trump in power is to claim that voters can decide to elect a dictator.
They cannot. Even if a majority of Americans attempted such thing (and remember, Mr. Trump received 3 million fewer votes than his opponent in 2016), the Constitution prohibits it.
The choice could not be clearer. Democracy is about means, while dictatorship is about ends. Mr. Trump uses any means available to achieve his own ends.
We can preserve our democracy and force Mr. Trump out of office. Or we can continue to struggle against someone who strives to thwart democracy for his own benefit.
In the months ahead, that choice will be made, one way or the other.
Robert Reich's latest book is "The Common Good," and his newest documentary is "Saving Capitalism."