If there’s one thing the election of Donald Trump has shown, it’s the strength of our formal political institutions. Do you disagree? Consider that in many states at many times in history, a democratically elected person so manifestly unfit for office would not have been allowed to take office. Yet there is no real risk of the American “deep state” carrying out a coup d’état or otherwise preventing Mr. Trump’s inauguration later this week. Once our formal constitutional process for election of the President concluded on January 6 (when Congress certified the electoral vote tally), that was that. We should be enormously proud of the strength of our formal institutions.

So if, when Representative John Lewis said, a few days ago, “I don’t see this President-elect as a legitimate president,” he meant that Mr. Trump was not validly elected, then he was clearly and dangerously in the wrong. His comment would be dangerous in the same way that birtherism, the view that President Obama was constitutionally ineligible to be President because he was not a natural-born citizen of the United States, was dangerous: both views undermine confidence in the formal constitutional mechanisms that have allowed us to prosper for more than two centuries.

But maybe Representative Lewis had something else in mind. Maybe he didn’t mean that Mr. Trump’s election somehow violated the written constitution, but that his actions before and after election have violated the unwritten constitution. Maybe the phrase is a little misleading. The unwritten constitution is not the law. It’s the norms, expectations, and traditions that let the government work. Every country has an unwritten constitution in this sense.

How could we make sense of Rep. Lewis’s comment if this second reading is right? Here are some thoughts.

• The unwritten constitution requires the President to hold press conferences attended by the press and to answer reporters’ questions, or give good reasons for not answering them. A press conference is not a rally, and supporters should not be cheering from the sidelines.
• The unwritten constitution requires that the press corps have offices in the White House, where they can meet and interact with senior officials.
• The unwritten constitution requires the President to listen to his advisers and respect their expertise, and the idea of expertise.
• The unwritten constitution requires the President to speak respectfully about members of Congress, the press, and private citizens, even if they disagree with him or don’t speak respectfully about him.
• The unwritten constitution requires the President to speak carefully, especially when speaking about foreign or military affairs, so that our intentions are clear to our allies and to our adversaries.
• The unwritten constitution requires the President to arrange his financial and business affairs so that he has no actual or apparent conflicts of interest.
• The unwritten constitution requires the President to have a legislative program. If his party controls Congress, he works with the majority leadership to craft his program. If not, he seeks to negotiate with the majority.

Notice what I didn’t say. The unwritten constitution does not require government-mandated health insurance. The unwritten constitution does not require open borders with Mexico, or that people in the country illegally should be able to stay. The unwritten constitution does not require sensible gun control laws or that we sign free trade deals. In short, for Democrats, we need to distinguish between the polices that a President Pence or a President Ryan might try to enact—we don’t like them, but we’re in the minority—and challenges to our unwritten constitution. For Republicans, we need to enact our program and yet have the courage to carry out our oversight responsibilities and to stand up to Trump when he challenges our unwritten constitution.

President Obama, in his farewell address, said some of this much better than I could when he pointed out the importance of animating the written Constitution with the values of our unwritten constitution:

Our Constitution is a remarkable, beautiful gift. But it’s really just a piece of parchment. It has no power on its own. We, the people, give it power. We, the people, give it meaning. With our participation, and with the choices that we make, and the alliances that we forge. Whether or not we stand up for our freedoms. Whether or not we respect and enforce the rule of law. That’s up to us. America is no fragile thing. But the gains of our long journey to freedom are not assured.