As a young man, Congressman John Lewis, who represents most of Atlanta, literally put his life on the line in pursuit of justice. As a key civil rights leader, he endured multiple beatings. Most famously, he led the demonstration that came to be known as Bloody Sunday, suffering a fractured skull at the hands of state troopers. Public outrage over that day’s violence helped lead to the enactment of the Voting Rights Act.

Now Mr. Lewis says that he won’t attend the inauguration of Donald Trump, whom he regards as an illegitimate president.

As you might expect, this statement provoked a hysterical, slanderous reaction from the president-elect – who, of course, got his start in national politics by repeatedly, falsely questioning President Obama’s right to hold office. But Mr. Trump — who has never sacrificed anything or taken a risk to help others — seems to have a special animus toward genuine heroes. Maybe he prefers demonstrators who don’t get beaten?

But let’s not talk about Mr. Trump’s ravings. Instead, let’s ask whether Mr. Lewis was right to say what he said. Is it O.K., morally and politically, to declare the man about to move into the White House illegitimate?

Yes, it is. In fact, it’s an act of patriotism.

By any reasonable standard, the 2016 election was deeply tainted. It wasn’t just the effects of Russian intervention on Mr. Trump’s behalf; Hillary Clinton would almost surely have won if the F.B.I. hadn’t conveyed the false impression that it had damaging new information about her, just days before the vote. This was grotesque, delegitimizing malfeasance, especially in contrast with the agency’s refusal to discuss the Russia connection.

Was there even more to it? Did the Trump campaign actively coordinate with a foreign power? Did a cabal within the F.B.I. deliberately slow-walk investigations into that possibility? Are the lurid tales about adventures in Moscow true? We don’t know, although Mr. Trump’s creepy obsequiousness to Vladimir Putin makes it hard to dismiss these allegations. Even given what we do know, however, no previous U.S. president-elect has had less right to the title. So why shouldn’t we question his legitimacy?

And talking frankly about how Mr. Trump gained power isn’t just about truth-telling. It may also help to limit that power.

It would be one thing if the incoming commander in chief showed any hint of humility, of realizing that his duty to the nation requires showing some respect for the strong majority of Americans who voted against him despite Russian meddling and the F.B.I.’s disinformation dump. But he hasn’t and won’t.

Instead, he’s lashing out at and threatening anyone and everyone who criticizes him, while refusing even to admit that he lost the popular vote. And he’s surrounding himself with people who share his contempt for everything that is best in America. What we’re looking at, all too obviously, is an American kakistocracy — rule by the worst.

What can restrain this rule? Well, Congress still has a lot of power to rein the president in. And it would be nice to imagine that there are enough public-spirited legislators to play that role. In particular, just three Republican senators with consciences could do a lot to protect American values.

But Congress will be much more likely to stand up to a rogue, would-be authoritarian executive if its members realize that they will face a political price if they act as his enablers.

What this means is that Mr. Trump must not be treated with personal deference simply because of the position he has managed to seize. He must not be granted the use of the White House as a bully pulpit. He must not be allowed to cloak himself in the majesty of office. Given what we know about this guy’s character, it’s all too clear that granting him unearned respect will just empower him to behave badly.

And reminding people how he got where he is will be an important tool in preventing him from gaining respect he doesn’t deserve. Remember, saying that the election was tainted isn’t a smear or a wild conspiracy theory; it’s simply the truth.

Now, anyone questioning Mr. Trump’s legitimacy will be accused of being unpatriotic — because that’s what people on the right always say about anyone who criticizes a Republican president. (Strangely, they don’t say this about attacks on Democratic presidents.) But patriotism means standing up for your country’s values, not pledging personal allegiance to Dear Leader.

No, we shouldn’t get into the habit of delegitimizing election results we don’t like. But this time really is exceptional, and needs to be treated that way.

So let’s be thankful that John Lewis had the courage to speak out. It was the patriotic, heroic thing to do. And America needs that kind of heroism, now more than ever.