Zohran Mamdani is a great example. He beat the Dems on their own grounds. I have faith he can be a leader against the Republican administration precisely because he proved he has a plan and the ability to execute it in spite of resistance.
We need to get rid of "first past the post" election systems. That will allow candidates like Mamdani to be competitive in a larger variety. The way I see it, this will NEVER happen through Republicans and as the system exists now there are only two viable choices. I'm not saying it won't be an uphill battle, but at least there has been some progress in making elections more representative of a variety of political views under Democrats.
Look, Bernie was the only political race ever where I donated money, so when I say this know where I am coming from. We have no idea if Bernie would have been any more effective than Biden if elected. Maybe the right would have reacted so hard that he would have been obstructed every step of the way, accomplished nothing, and we would have gotten Trump anyway. Maybe they would have just killed him in the first year and we would have ended up in the Civil War 2.