For decades, the United States’ extended nuclear deterrent has backstopped nuclear stability and supported nuclear nonproliferation among U.S. allies. Nuclear-sharing agreements and security guarantees have solidified nuclear deterrence, and combined conventional exercises have helped allies and partners feel secure in the face of hostile adversaries.

However, as the Trump administration openly reexamines the extent and depth of its alliance commitments, the credibility of the U.S. extended deterrent is fading. In response, the acquisition of sovereign nuclear capabilities has emerged as a legitimate policy pursuit in Japan, Korea, and Ukraine. These trends portend nuclear proliferation, threatening the nuclear balance and increasing the likelihood of nuclear use.

For decades, the United States’ extended nuclear deterrent has backstopped nuclear stability and supported nuclear nonproliferation among U.S. allies. Nuclear-sharing agreements and security guarantees have solidified nuclear deterrence, and combined conventional exercises have helped allies and partners feel secure in the face of hostile adversaries.

However, as the Trump administration openly reexamines the extent and depth of its alliance commitments, the credibility of the U.S. extended deterrent is fading. In response, the acquisition of sovereign nuclear capabilities has emerged as a legitimate policy pursuit in Japan, Korea, and Ukraine. These trends portend nuclear proliferation, threatening the nuclear balance and increasing the likelihood of nuclear use.

To address these assurance challenges and bolster deterrence, the Trump administration should restore a long-deteriorated aptitude: U.S. nuclear operations and signaling. Nuclear signaling is the visible, credible communication of a nation’s nuclear capability and resolve. Reinvigorating this skill means restoring the United States’ ability to quickly exercise or deploy tailored, visible, and........

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