https://www.politico.com/amp/news/2020/01/13/bernie-sanders-joe-biden-clash-2020-098433
The Sanders team’s expected assault comes as he is at the top of the polls in the first-in-the-nation caucus state of Iowa, but still significantly polling behind Biden among seniors. It’s not guaranteed he will execute the attack on Biden in a sustained way: After previous debates, some of his aides and supporters have been disappointed that he hasn’t confronted Biden more aggressively.