This morning, following a wellspring of reports about Joe Biden’s declining mental acuity, it became a very good time to be a Kamala Harris supporter. It’s been five days since Biden’s disastrous debate against Donald Trump, when he trailed off, got confused by simple questions, and could not for the life of him keep his mouth closed. His handlers have been trying to quell the calls for Biden to step down ever since he stepped off the stage — first...