The United States’ plans to sell the stealthy F-35 jet to a key NATO ally could allow Russia to study the most expensive weapons program in Pentagon history like a lab sample — a threat that has drawn the attention of several senators intent on protecting the pricey plane.

Turkey is just one of many NATO members that plans to buy the American-made F-35 Joint Strike Fighter, but it is the only country in the alliance that has also inked a deal to purchase the Russian-made S-400 missile defense system.

If those weapons systems worked in tandem, it could give the Russian military a front-row seat to the F-35’s capabilities — and, perhaps more importantly, its potential vulnerabilities.

“The F-35 and the S-400 are just nonstarters,” Sen. Lindsey Graham of South Carolina said shortly after visiting Turkey’s President Recep Tayyip Erdogan in Ankara.

Graham and fellow Republican James Lankford, along with Democrat Chris Van Hollen, are so opposed to the Turks mixing Russian missile defense systems with U.S. jets that they included a provision in the Senate’s Defense spending bill banning Turkey from acquiring F-35s if Ankara also purchases the Russian missile defense system.