New engine for F-35 would be too much of a gamble
While threats to U.S. national security continue to evolve, as they always do, they are as serious as ever. Potential Russian aggression in Ukraine, for instance, could threaten the hard-maintained European peace and the security of our European NATO allies. Rogue regimes such as Iran and North Korea, meanwhile, always present regional challenges that could erupt into something much larger.
Source: stripes.com