Sanders will be successful in his new Senate leadership post because he has the weight of the people behind him. Much of the grassroots supported Sanders. He has a lot of popular support. He will be successful because he can have a lot of influence with that kind of public support behind him.
Even though I was and still am a Clinton supporter, I think Sanders will do great in his Senate outreach role. I think his position will involve bipartisan discussions and that's where he will be an asset as I don't think all the Republicans are going to accept Trump with open arms.
It is unwise to judge a person's performance without proof, but Sanders is a veteran in the political landscape and it is highly likely that he will be adequate in the senate. He has displayed sound judgement in the past and does not seem to have overly radical views on most things.
Bernie Sanders will not be any more successful in his new Senate leadership post then he was in his past role as a senator, or in his bid to become president. Sanders is a radical kook who has no place in United States government. By all means, if he is the best Democrats can do then a party deserves everything it cats.