Remember, we dropped more bomb tonnage on North Vietnam than we did on Germany in WWII. And who won the Vietnam War? Bottom line - bombs don’t win wars by themselves.
Unless you can credibly threaten total nuclear annihilation like we did to the Japanese with atomic bombs. The NVA and the Vietcong knew that if we threatened them with the same, the Soviets would make us back down with a nuclear counter threat.
Vietnam was not lost on the battlefield