He's got two big demographic challenges blacks and older voters, which coincidently were two difficult nuts to crack for Sanders. Biden is very familiar, just as the Clintons were, he's been around awhile and fighting the good liberal battles for decades. Blacks still are not very engaged, and won't be until after Iowa because urban issues are not really discussed with focus until later and South Carolina is the first southern contest with a high black population. older voters tend to be a bit more cautious about radical social or political movements and that generation is more suspect of socialism and less comfortable with gay marriage, neither of which got a lot of good press in their younger days. Sanders grabbed the party's anti-Clinton vote ( there was no where else to go) and had the far left of the party and the nation to meld together with young and independent voters who were naturally suspicious of party loyalty and two party myopathy.
Buttigieg sells himself rather differently as representing a new generation both in vision and talent with a techno-savy and innovation centered approach to problem solving, rather than a European social democrat centered approach. But I agree he is unseasoned, and inexperienced on the big stage and we really don't know nearly enough yet beyond his clichés.
The point is that Iowa is a caucus, and passion and commitment is everything in a caucus state. Sanders was a fresh bowl of granola with nuts and berries four years ago, and well - the cereal is a bit soggy now and the oats have molded a bit. Its very difficult for an older flame to re-ignite twice on the same kindling. I don't know how Sanders does that and I think that is going to impede him especially among a younger college crowd. Sanders has literally plateaued in Iowa among likely caucus attendees. He was a 9% last survey in June. He still is. He's not making any headway there while Buttigieg has usurped him to 13%.
Speaking of those college kids that Sanders owned to himself in 2016. Well one thing about South Bend Indiana ,I ts most famous as the stomping ground of a few college kids
University of Notre Dame - Wikipedia I think Pete's pretty comfortable on a campus after graduating from Harvard University and then from Pembroke College, Oxford, on a Rhodes Scholarship. He is particularly adept at reflecting that vision.