If you’re referencing Bernie Sanders in 2016 and 2020, he wasn’t “democratically popular” in either race. That simply is not supported by polling or election results. He was well behind Clinton by all metrics. Then in 2020, he was briefly “winning” because several similar candidates were splitting the center-left lane. The moment the center-left lane narrowed, Sanders’ lead evaporated.
It’s SOP for candidates to more or less clear the field for an incumbent president. This is partially because of a perceived effect from a strong primary challenger weakening an incumbent. So Democrats were just doing what both parties have been doing for the last half century.
The change from Biden was in response to clear reactions from the US electorate. The electorate saw Biden’s debate performance and was not impressed. There wasn’t time to run a process, so Kamala was the obvious choice given a non-ideal situation. But the electorate got what it wanted in terms of an option that wasn’t elderly.
I’m not sure how to parse what you’re saying. As far as DNC rules are concerned, they “call” it once all primary races are held.
The Democratic primary uses proportional representation, so candidates don’t win states, they win delegates. Hillary Clinton got 55% of the popular vote, Bernie Sanders got 43%. There are no two ways to slice it, Bernie lost that election by the rules of a democratic election by a sizeable margin. Meanwhile, Hillary was dealing with getting hacked and Benghazi Benghazi Benghazi. And you’re forgetting the often adoring coverage that was played to audiences on the left about Sanders.
The selling point for Kamala wasn’t anything in particular about her. She’s the VP and was the only obvious choice. There was no appetite for a contested convention, which was the alternative. It was always going to be an uphill battle, so in a sense she’s also a sacrificial lamb.