'He is degrading': Trump biographer explains how he thinks ex-president's 'mind is slower'

Donald Trump has always been ignorant and irrational, but over the last few years, it's clear that he is slowing down and becoming less coherent, according to the former president's own biographer.

Tim O'Brien, who spent massive amounts of time with Trump before writing TrumpNation: The Art of Being the Donald, appeared on MSNBC on Saturday to discuss Trump's recently reported "exhaustion."

The host played videos of Trump slurring his words and failing to finish his sentences, and asked O'Brien his opinion.