As a New Jerseyite, just because people dont think he deserves re-election doesnt mean they wont vote for him. Literally the only person I can see taking Menendez down in the primary is Richard Codey. A leftwinger from the Bernie wing needs to be able to win over working class minorities from Menendez, something I dont think will happen. Anybody thinking Menendez is as weak as Lautenberg would probably have a point if there was another Cory Booker, but theres not.
Yeah a primary challenger would really have to run up huge margins in Southern Jersey probably just to win against Menendez and I don't think it could be done.