I believe that the move to Biden is more from seniors that voted Obama 2008 (and subsequently moved Republican in 2012 and 2016). They are dissatisfied with the Trump performance on COVID-19 and more receptive to Biden.
It won't be enough in MO, but it's an indicator on how the Rust Belt and Midwest will respond--good swings to the Democrats in November.
Missouri went R because of the Religious Right, and southern Missouri is still Mountain South. Its one significant minority, blacks, is not growing. St. Louis is basically "Detroit on the Mississippi". If St,. Louis suburbs are going D then they do so by taking in former residents of St. Louis.
