Do you have evidence to back up the assertion that his positions have shifted in response to polling? The example I often see is his "Medicare for All who want it" plan which I responded to below (in https://news.ycombinator.com/item?id=21315147).

From the beginning he stated his campaign would first lay a foundation of ideals, then build policies from there. In my view, that's what he's done over the last 9 months.

I have no connection to the campaign, but I'm sure someone reading does. Can you say more about what has turned you off recently?