For several reasons, the United States must not ratify the CTBT before validating the safety, security, reliability and effectiveness of U.S. nuclear weapons as predicted by the stockpile stewardship program. First, testing is the most effective and lowest risk way to ensure the safety, security, reliability and effectiveness of the current U.S. stockpile. Testing is also needed to address the increasing risk of certifying the U.S. nuclear stockpile due to the combination of incremental changes introduced to refurbished nuclear weapons and the effects of aging. Testing would enable the acquisition of nuclear data that would validate and significantly enhance the stockpile stewardship program, perhaps make testing unnecessary in the future. A test program could improve the security of U.S. nuclear weapons, and would enable the testing and verification of improvised nuclear device designs as well as techniques to disable those weapons. Finally, testing is the only effective way to develop and maintain nuclear weapon-related competencies such as containment, instrumentation and nuclear forensics that took decades and billions of dollars to develop.