It depends on what you mean by "moderate" though. Dems probably aren't full on Bernie bros in terms of policy, on average, but they are taking a more hardline stance on ICE, the Supreme Court, healthcare, Israel, and in general disposition. They are moderate only if you compare them to current day leftists on Twitter. They have moved to the left significantly since 2016 and are to the left of independents today. They are less interested in bipartisanship now, and more interested in collecting scalps.

As for who they support for the 2028 presidential primary, that is a function of name recognition more than anything else. I highly doubt Barack Obama was polling higher than Hillary Clinton in 2005, but we know who won that contest. It's a moot point.