This scenario is actually only possible if Biden dies between now and 2024 and Kamala Harris gets a massive sympathy bump (which she would).
Here's a possible scenario that I hope doesn't happen:
Biden runs again, Republicans nominate either Trump or someone just as ridiculous after a primary battle that leaves the old guard of the party shut out at the RNC. However, a day after the Republican nominee talks about 'golly it would be great if I didn't have an opponent, might one of you be able to help with that?' or something similar, one of his supporters/long time Republican assassinates Biden. They are captured alive and right up until election day claim they were just trying to save America because the Republican nominee told him too. The Dems nominate Harris (or really anyone they like) at the convention after the attack and throughout the campaign show case the fixes they've made since the start of the Biden presidency while slamming the Republicans as cultivating a murder cult, warning that giving them power again risks emboldening more killers. The result isn't a repeat of '64, but election night is short and the outcome well known before the west coast closes their polls. And despite this electoral outcome, the Republican party decides to ignore the obvious lessons and continues to embrace violent extremist rhetoric in 2028.
