Taiwan's efforts to strengthen its military capabilities are being hampered by growing uncertainty over whether the United States would actually come to its defence in a crisis, making it politically and strategically harder for Taipei to justify large arms purchases. When confidence in a security guarantor wavers, the domestic case for spending heavily on that guarantor's weapons systems weakens alongside it, creating a self-reinforcing slowdown in defence readiness. The situation underscores a broader challenge for US alliances in the Indo-Pacific: credibility gaps do not merely affect diplomacy — they have direct, measurable consequences for the military preparedness of partners on the front line.