MS NOW’s Lawrence O’Donnell expressed his concerns about Donald Trump’s cognitive health, saying any deterioration would amount to the biggest story in the world “because everything else follows from that, everything.”

“No matter what the news of the day is, if the president of the United States is insane, that is the biggest news of the day or any day,” O’Donnell began his monologue. “That is what will live in history. That is what historians will devote their attention to if the president of the United States is insane.”

Trump has not publicly been diagnosed with a cognitive disorder, and O’Donnell is not a doctor.

But the “Last Word” anchor argued that changes in the way Trump speaks and tells stories deserve greater scrutiny, pointing to a claim the president made during a midterm campaign rally in Texas that his wife, first lady Melania Trump, had addressed him as “sir,” which is usually the starting point for what O’Donnell described as hallucinated interactions from the president.

“Nine years ago, I tweeted, if Trump gets dementia how will we know? This is how we will know,” O’Donnell said. “We will catch these seemingly small slips in his lying process, in his speaking process, and we will notice that that is not the kind of thing he could have said nine years ago or seven years ago or five years ago or even two years ago.”

“Maybe any one of those slips is not a reflection of cognitive ability but the accumulation of them might be, and that is why I focus on them here also because no one else does,” he added.

Watch O’Donnell’s full analysis here: