If our nuclear weapons are not reliable, they are not much of a credible deterrent and the nuclear umbrella that we and our allies count on for our mutual defense will have gaping holes in it. We have to face reality. Our nuclear stockpile is aging. Our nuclear inventory is older than it has ever been and nuclear materials and components degrade in unpredictable ways, in some cases causing weapons to fail. Reliability would suffer.
Safety is also essential.
A permanent ban on testing would jeopardize the safety of our nuclear arsenal by preventing us from integrating the most modern, advanced safety measures into our weapons. Even now, our nuclear arsenal is not as safe as we could make it. Of the nine weapons systems currently on hand, only one employs all of the most modern safety and security measures available. Safety modifications of this kind would require testing to make sure they work as intended. Sure, advocates of this treaty argue that there are other means of testing a weapon's safety and reliability.