But Pentagon insiders say even this is unlikely to sink the project. A likelier casualty: Marine Corps commandant Gen. James L. Jones’s chances of making chairman of the Joint Chiefs of Staff after the current chairman retires this fall. Jones, who has remained a staunch supporter of the aircraft, may have been tainted by its troubles. While no one believes that he ordered doctored records, sources say powerful senators are pushing investigators to find out why the Marines testing the tilt-rotor aircraft thought the stakes were so high that they had to lie. Said one congressional source: “The issue is the expectations set for this program and who set them.”