Donald Trump must be the biggest liar in the history of American politics, and that’s saying something.

Trump lies the way other people breathe. We’re used to politicians who stretch the truth, who waffle or dissemble, who emphasize some facts while omitting others. But I can’t think of any other political figure who so brazenly tells lie after lie, spraying audiences with such a fusillade of untruths that it is almost impossible to keep track. Perhaps he hopes the media and the nation will become numb to his constant lying. We must not.

Trump lies when citing specifics. He claimed that a “tremendous flow of Syrian refugees” has been entering the country; the total between 2012 and 2015 was around 2,000, barely a trickle. He claimed that “we have no idea” who those refugees are; they undergo up to two years of careful vetting before being admitted.

Trump lies when speaking in generalities. He claimed that President Obama “has damaged our security by restraining our intelligence gathering and failing to support law enforcement.” Obama actually expanded domestic intelligence operations and only dialed them back because of bipartisan pressure following the Edward Snowden revelations.

Trump lies by sweeping calumny. “For some reason, the Muslim community does not report people like this,” he said of Omar Mateen, the shooter in the Orlando massacre. But according to law enforcement officials, including FBI Director James Comey, numerous potential plots have been foiled precisely because concerned Muslims reported seeing signs of self-radicalization.

Trump lies by smarmy insinuation. “We’re led by a man that either is not tough, not smart, or he’s got something else in mind,” he said of Obama. “There’s something going on — it’s inconceivable. There’s something going on.” He also said of Obama: “He doesn’t get it, or he gets it better than anybody understands. It’s one or the other, and either one is unacceptable.”

You read that right. The presumptive Republican nominee implies that the president of the United States is somehow disloyal. There is no other way to read “he gets it better than anybody understands.”

Trump claims that Hillary Clinton, the all-but-certain Democratic nominee, “wants to take away Americans’ guns, and then admit the very people who want to slaughter us.” Clinton has made clear that she doesn’t want to take anyone’s guns away; nor does she want to eliminate the Second Amendment, as Trump also claims. And the idea that Clinton actually wants to admit would-be slaughterers is grotesque.

I write not to defend Obama and Clinton, who can speak for themselves — and have done so. My aim is to defend the truth.

Political discourse can be civil or rowdy, gracious or mean. But to have any meaning, it has to be grounded in fact. Trump presents a novel challenge for both the media and the voting public. There is no playbook for evaluating a candidate who so constantly says things that objectively are not true.

All of the above examples come from just five days’ worth of Trump’s lies, from Sunday to Thursday of this week. By the time you read this, surely there will have been more.

How are we in the media supposed to cover such a man? The traditional approach, which seeks fairness through non-judgmental balance, seems inadequate. It does not seem fair to write “Trump claimed the sky is maroon while Clinton claimed it is blue” without noting that the sky is, in fact, blue. It does not seem fair to even present this as a “question” worthy of debate, as if honest people could disagree. One assertion is objectively false and one objectively true.

It goes against all journalistic instinct to write in a news story, as The Washington Post did Monday, that Trump’s national security address was “a speech laden with falsehoods and exaggeration.” But I don’t think we’re doing our job if we simply report assertions of fact without evaluating whether they are factual.

Trump’s lies also present a challenge for voters. The normal assumption is that politicians will bend the truth to fit their ideology — not that they will invent fake “truth” out of whole cloth. Trump is not just an unorthodox candidate. He is an inveterate liar — maybe pathological, maybe purposeful. He doesn’t distort facts, he makes them up.

Trump has a right to his anger, his xenophobia and his bigotry. He also has a right to lie — but we all have a duty to call him on it.

Eugene Robinson’s email address is eugenerobinson@washpost.com.