Threat levels are cyclical, and the periods when counter-terrorism capacity looks excessive are precisely the periods when it is working. Supporters argue that dismantling authorities and infrastructure during quiet years is how gaps reopen, and that rebuilding is slower than losing. Critics respond that this argument is unfalsifiable, since any level of capability can be justified by a threat that has not materialised, and that it has been used to defend every expansion since 2001. Neither side can prove what would have happened under the alternative.