POLITICIANS LIE all the time, it is sometimes said. Never before has an American politician come as close as Donald Trump has to making the saying literally true.

Despite what you may have heard at Sunday night’s presidential debate . . .

Syrian refugees are vetted before they enter the country.

Americans are taxed at lower rates than the citizens of many other developed countries.

Mr. Trump publicly backed the Iraq War before the invasion. His claims otherwise have been repeatedly debunked.

The Fact Checker’s Glenn Kessler and Michelle Ye Hee Lee round up suspect claims from Donald Trump and Hillary Clinton. (The Washington Post)

The Immigration and Customs Enforcement agency has not endorsed Mr. Trump.

The country’s nuclear arsenal is not “exhausted.”

The U.S. economy is growing at faster than 1 percent per year.

There has been hacking of U.S. email accounts this election year. The U.S. intelligence community has blamed the Russian government.

Mr. Trump did urge his Twitter followers to “check out” an alleged sex tape involving former Miss Universe Alicia Machado.

Hillary Clinton is not responsible for the racist “birther” campaign Mr. Trump waged against President Obama.

She did not laugh at a rape victim.

“Clean coal” is a contradiction in terms.

The trade deficit was not $800 billion last year.

Ms. Clinton has not proposed admitting “hundreds of thousands” of Syrian refugees.

She does not favor a single-payer health-care plan.

Most health-care premiums are not spiking by “68 percent, 59 percent, 71 percent.”

The Islamic State does not control “a good chunk” of Libya’s oil.

The North American Free Trade Agreement was not a “disaster” for jobs.

Ms. Clinton did not order the deletion of State Department emails after they were under subpoena.

U.S. Ambassador J. Christopher Stevens did not make 600 calls for help before dying in the September 2012 Benghazi attacks.

The United States is not “giving” Iran $150 billion as part of the nuclear deal.

There is no evidence “many people saw the bombs all over the apartment” of the San Bernardino, Calif., shooters.

Most African Americans do not live in bombed-out inner cities.

Earlier this year, Politico subjected a week’s worth of Trump campaigning to its magazine’s fact-checking procedure and found that Mr. Trump averaged about one misstatement every five minutes. By our reckoning, he far exceeded that pace Sunday night.

Last week we published a series of editorials on the damage Mr. Trump could do if he were president. But no one should minimize the damage he has already done. One casualty is the old-fashioned idea that, whatever the cynical proverb, politicians should not routinely lie.