The stream of lies, half truths and exaggerations keeps coming from President Donald Trump, three weeks deep into his administration.

The big unanswered question: Will he ever dial it back, and if he doesn’t, will Americans who have staunchly defended him to this point keep doing so? Will the lies eventually weaken the popular support he needs to advance his agenda?

Even those who have supported his goals of controlling immigration, fixing Obamacare, negotiating fair trade agreements and draining the swamp in Washington have to begin wondering whether his habit of uttering and tweeting statements that are demonstrably false will extend to his campaign promises as well. Will he be able to deliver on them?

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There is nothing unique about presidents lying. They all have done it, and some have been whoppers. President Obama falsely promised about Obamacare, “If you like your health plan you can keep,” “If you like your doctor, you can keep him” and it will save families lots of money. George W. Bush said Iraq had weapons of mass destruction. Bill Clinton insisted he “did not have sex with that woman.” George H.W. Bush made a promise he couldn’t keep: “Read my lips; No new taxes.” Ronald Reagan said he was unaware of the Iran-Contra deal. Richard Nixon said he wasn’t a crook. And Lyndon Johnson said attacks on two U.S. ships in the Gulf of Tonkin were unprovoked.

With Trump, though, there is a big difference. He lies habitually. And even in the face of overwhelming evidence that what he said is false, he will never concede the point. He simply repeats the lie, apparently secure in the knowledge that if you state a falsehood frequently enough, lots of people — particularly those who want to believe you — will swallow it whole.

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Since Trump’s swearing in alone, here are some of his lies:

•The murder rate in our country is the highest it’s been in 47 years.” While the rate has increased each of the past two years, it hasn’t been nearly enough to reverse a decades-long downward trend.

•Terrorism and terrorist attacks in the U.S. and Europe have gotten to a point where it’s not even being reported.” This is demonstrably untrue.

•Three million people voted illegally in the last presidential election, most of them for Hillary Clinton. This has been repeatedly debunked by a variety of reliable, independent sources.

•He can’t release his tax returns until an IRS audit is completed. There is no such IRS prohibition.

•No one cares whether he releases his tax returns but the press. An ABC News/Washington Post poll last month found 74 percent of Americans say he should release his tax records.

•“Sanctuary cities” are hotbeds of crime. The opposite is true.

There is nothing new about Trump’s habitual lying. There is, of course, the Barack Obama birther myth he helped perpetuate and his repeated lies about his recollections of 9/11: the people he saw falling from the Twin Towers four miles away from his office, the “hundreds of friends” he said he lost that day and the Muslim mobs he saw celebrating in New Jersey.

The pattern was established long before Trump campaigned for president. But now that he has ascended to the presidency, the lies could be his undoing. Credibility is essential, not only to gaining the backing needed to advance his agenda in Congress and building public support for it, but in establishing trust abroad.

Unfortunately, there is little evidence that his handlers are working to rein him in. His two most visible spokespersons, Sean Spicer and Kellyanne Conway, have not helped soften the damage of his lies, often doubling down on them and being combative with the press.

Will Trump change? Can he change? Much of his appeal has derived from his outspokenness, his lack of political correctness and his willingness to talk back to those he and his supporters believe deserve it. Those attributes certainly helped get him elected. But, in combination with his pattern of lies, they could prove to be a fatal weakness if he doesn’t soon adapt to his new circumstances as the leader of the most powerful nation on earth.

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