"Donald Trump lies because he knows he can get away with it," O'Donnell said on "The Last Word," highlighting the interviewing techniques of anchors on Sunday morning news programs. "The most impolite candidate in American political history relies on the politeness of his interviewers to get away with lying."
O'Donnell then showed a clip of ABC News' "This Week" in which host George Stephanopoulos pressed Trump over his claims that he saw "thousands and thousands" of Arabs cheering in New Jersey after the World Trade Center collapsed on 9/11, but fell just short of calling Trump's assertion a lie.
"Donald Trump knows that George can't tell his audience that Trump is lying there, because the industry convention of Sunday political chat is that they never call a lie a lie," O'Donnell said. "That's just too impolite for Sunday mornings and Trump exploits that politeness."
Politeness isn't the only reason interviewers go easy on Trump, he added.
"Donald Trump gets good ratings on these shows," he said. "If one of the hosts tells Trump he's lying in the middle of an interview, that host will never get another chance to interview Donald Trump again. But his competitors will."
While he criticized the way some programs have handled of Trump's false claims, he praised The Washington Post and The New York Times for publishing damning editorials about Trump this week.
The Washington Post called Trump's lying and bullying "dangerous."
"The growing ugliness of Donald Trump’s campaign poses a challenge to us all," the paper's editorial board wrote. "We have seen the likes of him before, in the United States and elsewhere: narcissistic bullies who rise to prominence by spreading lies, appealing to fears and stoking hatred. Such people are dangerous."
The New York Times took on Trump's many egregious claims.
"In the Republican field, Mr. Trump has distinguished himself as fastest to dive to the bottom," its editorial board wrote. "If it’s a lie too vile to utter aloud, count on Mr. Trump to say it, often."
O'Donnell issued a warning to journalists who will cover Trump in the future.
"The time has come for Donald Trump’s TV interviewers to tell him that he is lying as soon as he floats his next lie on TV," he said. "If they don’t, they risk becoming accomplices of a lying demagogue."
Watch the "Last Word" clip above.
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