Please don't anyone get too excited about poll leads now. Hillary was very far ahead

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31. For whatever reason that poll isn't in the RCP average

and it is better than every single poll that is in it for her. But even then, she still doesn't break 50, Biden does in over half of the polls in 2020. Her poll result in that poll in terms of support would be Biden's third worst poll (tied with one other). Trump actually does better in that poll than his typical result for that time frame (it would be tied with several for his 2nd best). But this time it would be tied for his worst. There are considerably fewer undecided voters and Biden is breaking 50 in a majority of polls and in average. She didn't break 50 in even one poll. Trump's RCP average now is 41.4 vs the 46.1 he got in 2016.

I do agree with your reasons for why Biden is doing better in many cases. Clinton was certainly victimized by gender, no arguing that. I also think she was a press target for years and years while Biden mostly hasn't been in part due to her being the wife of Bill Clinton who was a rather large press target in his own right. I also think that Sanders has been considerably more constructive this time than last time. But that doesn't diminish the fact that he is clearly doing better in these polls than Clinton was 4 years ago by both measure of total support and margin. While the increase in margin isn't huge the increase in total support is larger and crosses the all important 50%.