The US military disrupted GPS signals over the western US for two weeks in late January to train for exactly this scenario. It was part of their “Red Flag” wargames training.
From the article:
>GPS denial is a becoming a huge issue for American military planners. Peer states, especially Russia, are already putting GPS spoofing and jamming tactics to work during various training events near their own borders. We have discussed this situation in great depth before, and I would suggest you read this article to understand just how deeply the loss of reliable global positioning system data can mean for the U.S. and its allies during a time of war, as well as what is being done to overcome such a monumental hurdle.
Also:
>The disruptions will begin on January 26th and will run through February 16th. Flying.com reports: "The NBAA Command Center reports the U.S. military will begin training exercises on the Nevada Test and Training Range between 0400Z until 0700Z daily. Training maneuvers will impact vast portions of the Western U.S. including California, Nevada, Oregon, Wyoming, Arizona, Utah, Colorado, Montana and New Mexico. FAA enroute ATC centers affected include Albuquerque (ZAB), Denver (ZDV), Los Angeles (ZLA), Salt Lake (ZLC), Oakland (ZOA) and Seattle (ZSE). Operations in R-2508 and R-2501 may also be impacted.
http://www.thedrive.com/the-war-zone/17987/usaf-is-jamming-gps-in-the-western-u-s-for-largest-ever-red-flag-air-war-exercise