Britain cooperates with France on warhead work and relies on the United States for Trident missile support, so replacing the American element could create excessive dependence on France. That logistical reliance differs from claims that the United States can simply disable a Trident missile. A jointly developed missile with production in both countries is one possible hedge. More broadly, the disappearance of American guarantees and enforcement could make independent nuclear deterrents more attractive to capable but exposed states, increasing open proliferation.
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Trident replacement and a wider proliferation risk
An American withdrawal would force an early British missile decision and could weaken the security guarantees that restrain other states from seeking nuclear weapons.