He was firing on all his (remaining) cylinders.

Kamala was (relatively) more popular when she was performatively distancing herself from Biden. Now that she’s changed tack and moved in lockstep with Biden and his brand of centrist fascism, she’s become unpopular.

The author of this article thinks the only reason Biden wasn’t viable was because of that debate performance. This ignores the fact that Biden was already even less popular than Trump was at this point in his presidency, and well below where LBJ was when he figured he was too unpopular to win reelection and dropped out.