To understand why the Pentagon isn't placing such redundant backups on priority one is something that needs to be looked at in a variety of ways.
Firstly, the Pentagon is well aware that Russia and China are focusing on technology that will interfere with electronic equipment. Yet the reason why they aren't actively developing such technology is because there is no impending need to launch a land invasion of either Russia or China.
That's right. The only place where current tech will allow electronic scrambling equipment to be used is on the home field. And America certainly isn't planning a land invasion of Russia or China anytime soon. In fact, all three countries are actively interested in avoiding war with each other.
The Pentagon's actual threat is currently in the form of North Korean nuclear missiles. In case you haven't heard, North Korea now has the capability to reach the US Mainland with their missiles and is threatening US military bases and allies in Japan and South Korea.
Redundant backup weapons systems are the least of the US Armed Forces' priorities at the moment.