BRIAN STELTER (HOST): We are all only as good as our sources of information. We make decisions about how to vote and who to believe based on the information we consume. That's why we need, pardon the use of the title here, reliable sources. And that's why I cringe when I hear Donald Trump reciting conspiracy theories. This is harmful no matter how well journalists debunk what he says. Case in point, this week the National Enquirer story alleging a link between Ted Cruz's father and JFK assassin Lee Harvey Oswald. This is unproven. Just to be clear, there's no evidence to believe it's true and there is lots of evidence to believe it's not true. But the conspiracy theory showed up first on fringe, right-wing websites this time last month. Then it made its way to the Enquire,r and then made its way to Donald Trump's mouth.

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The most troubling part of that, I think is when Trump accuses the press of covering up this horrible family secret. Later in the day CNN's Jake Tapper fact-checked him on that.

[BEGIN VIDEO]

JAKE TAPPER: We in the media don't talk about it because there's no evidence of it. … . So any suggestion that Cruz's father played a role in the Kennedy assassination is ridiculous and, frankly, shameful. Now that's not an anti-Trump position or a pro-Cruz position. It's a pro-truth position.

[END VIDEO]

STELTER: Tell me if you agree. I think it's pretty unusual to see something like that on TV, but it shouldn't be. Because by re-tweeting false information or repeating what he reads on obscure websites, Trump represents a unique challenge for the press. Before we go any further, let's be honest, right, Trump is far from the only politician who tells exaggerated stories or depends on dubious statistics. But he is the only one who repeats a smear that was on the front page of the National Enquirer tabloid. The journalists who fact-check him every day say he is categorically different from all the rest of the contenders out there. Now Trump later said that he was just counter punching because Cruz's father had attacked him. He said he didn't believethe Enquirer story, but he thought people should know about it. Remember, Trump has been doing this for a long time. He bought into the birther conspiracy, repeatedly saying that President Obama was not born in the United States. In some ways that led to his rise among conservatives. More recently, Trump cited grossly inflated numbers of Syrian refugees being relocated in America, and he falsely said that thousands of people in New Jersey cheered on the day of the 9/11 attacks.

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That story has circulated via chain email letters for years, you know the ones that you get from your relatives.

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To be clear again, that did not happen. If lots of people had been cheering in Jersey it would have been a huge story and we would have the video and we would play that video right now. To be fair to Trump, he has not repeated that 9/11 claim in a long time, but he has invoked other conspiratorial ideas. Back in March, he wrongly claimed that this protester who rushed the stage at one of his rallies had, quote, “ties to ISIS.” Chuck Todd tried to tell him that he'd been tricked by a hoax website.

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It doesn't seem like he distinguishes between Meet the Press and the National Enquirer. And I think it's important to recognize here that many voters don't either. We can't put our heads in the proverbial sand and pretend like this misinformation is out there. We have to address it head-on as journalists. I think a lot of us see a lot to like about Trump, a lot to admire about his campaign, but not his tendancy to believe this misinformation, and these hoaxes, and these conspiracy theories. But here's the thing, this is the important part. I could sit here and tell you about how some news outlets have higher standards than others. Some people will believe me and some people won't. But mistakes, and self-inflicted wounds, and the lowering of standards across the board have lowered trust in media overall, and made it tougher for us to hold all candidates accountable. Now I hope that forceful rebuttals, like the like the ones we saw here from Tapper, and Stephanopoulos, and Todd, are part of the solution, because as Seth Meyers predicted this week we'll be hearing more conspiracy theories this fall.