The problem the F-35 poses for the US is that as always with Lockheed programs it is way over cost. This is forcing cuts in production and thwarting foreign sales. Aviation Leak has not yet released this story but had reported that the hold-up was whether the US would provide source code for all of the F-35 software.
Report: Iran's Culture Ministry refuses to allow Barenboim to perform in Tehran (DPA)
from the article: Israel to purchase 20 Lockheed Martin F-35 fighter jets