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Hillary Clinton needs to step into an unconventional role tonight: fact-checker.

On Saturday, The New York Times published a compendium of all the falsehoods Donald Trump had uttered in the previous week—a list of lies so long and outlandish that Republican strategist Mike Murphy called it the “unreality bubble that he surrounds himself with.” It ranged from fibs about his opposition to the Iraq War to blatant falsehoods about his support among Hispanic and African-American voters.

We are likely to see the same unvarnished, unapologetic fibber on stage at Hofstra tonight. Of course, most presidential candidates stretch the truth a little during debates. But few candidates have ever traded in lies of the same magnitude and with the same frequency as Trump. “He believes debates are not won or lost on policy minutiae,” the Times wrote of his debate prep last week. “His advisers see it as a waste of time to try to fill his head with facts and figures.”

But more worrying even than his proclivity to stretch the truth is the possibility that no one will call him out on his biggest whoppers. Candy Crowley was vilified when she corrected Mitt Romney on stage in 2012, and newscasters have generally held back from correcting candidates outright. Janet Brown, the director of the Commission on Presidential Debates, has said, “It’s not a good idea to get the moderator into essentially serving as the Encyclopedia Britannica.”

Trump has already warned Lester Holt, the NBC newscaster chosen to moderate the debate, not to correct him on specifics. And indeed, Holt is known for being studiously nonpartisan, and may not feel the need to correct Trump on stage. Furthermore, the networks have said they would not publish fact-checking on the screen during the debate (only Bloomberg TV is doing it).

That makes Hillary Clinton the only person who can engage Trump and call him out for peddling fabrications on stage.