Eleven minutes into the June 27 presidential debate, CNN anchor Dana Bash slipped a note to her colleague Jake Tapper after President Biden gave a rambling, incoherent answer. “He just lost the election,” she wrote. The event at the network’s Atlanta studios — recounted in Tapper’s and Axios correspondent Alex Thompson’s new book, “Original Sin: President Biden’s Decline, Its Cover-Up, and His Disastrous Choice to Run Again” — turned out to be the most consequential presidential debate in history. Negative reaction to Biden’s alarmingly disastrous performance led him to abandon his campaign three weeks later and Vice President Kamala Harris...