I'm not entirely convinced that Rothman independently chose to run in the Ninth District instead of taking on Garrett in the Fifth. Your "sponsors" often lend their opinion on how you should run your campaign and my guess is that donors balked at spending their money and possibly losing it if Rothman lost his re-election against Garrett. And that held great sway on his decision to take on Pascrell.
Rothman's first mistake was to characterize himself as the "Bergen County" representative. Clifton, Paterson, and Passaic will not believe that he will have their interests in D.C. primarily. He wants their votes but he may not deliver the money and services that Pascrell currently does.