Eh, I was curious and did some more research. Look at Sherrod Brown (D-Ohio), Bob Casey Jr. (D-PA), and Amy Klobuchar (D-MN), all of whom have been serving similar amount of time - they have sponsored bills over 1k, co-sponsored ranging from 3k to 8k. Compare that to Bernie's ~ 200 co-sponsored and 3 sponsored ... I'd say thats a very weak performance compared to his peers.