Beyond candidate quality, it's striking how terrible the Menendez campaign is as an operation. This is probably partly a product of Menendez's own flaws, though. What credible operative would want to work for this scumbag?
New Jersey has very unusual politics. Unlike with Democrats who have lost in New Jersey, like Corzine, who was abandoned by the county machines in favor of Christie, Menendez has the full backing of the county machines, so there's a lot of operatives out there working in his favor.