We consider the Ising perceptron with gaussian disorder, which is equivalent to the discrete cube t´1,`1u N intersected by M random half-spaces. e perceptron's capacity is α N " M N {N for the largest integer M N such that the intersection in nonempty. It is conjectured by Krauth and Mézard (1989) that the (random) ratio α N converges in probability to an explicit constant α‹ . " 0.83. Kim and Roche (1998) proved the existence of a positive constant γ such that γ ď α N ď 1´γ with high probability; see also Talagrand (1999). In this paper we show that the Krauth-Mézard conjecture α‹ is a lower bound with positive probability, under the condition that an explicit univariate function S‹pλq is maximized at λ " 0. Our proof is an application of the second moment method to a certain slice of perceptron con gurations, as selected by the so-called TAP ( ouless, Anderson, and Palmer, 1977) or AMP (approximate message passing) iteration, whose scaling limit has been characterized by Bayati andMontanari (2011) and Bolthausen (2012). For verifying the condition on S‹pλq we outline one approach, which is implemented in the current version using (nonrigorous) numerical integration packages. In a future version of this paper we intend to complete the veri cation by implementing a rigorous numerical method.Krauth and Mézard [KM89] conjectured that as N Ò 8 the ratio M N pκq{N converges to an explicit constant α ‹ pκq, which for κ " 0 is roughly 0.83. is was one of several works in the statistical physics literature analyzing various perceptron models via the "replica" or "cavity" heuristics [Gar87, Gar88, GD88, Méz89]. In particular, in the variant where J ranges not over t´1,`1u N but over the entire sphere of radius N 1{2 , the analogous threshold was computed by Gardner and Derrida [GD88]. Another common variation is to take g µ,i P t´1,`1u to be i.i.d. symmetric random signs (Bernoulli disorder). e conjectured thresholds di er between the Ising [KM89] and spherical [GD88] models, but do not depend on whether the disorder is Bernoulli or gaussian. While the classical problem is under Bernoulli disorder, we have chosen to work under gaussian disorder to remove some technical di culties. For the spherical perceptron, very sharp rigorous results have been obtained, including a proof of the predicted threshold for all nonnegative κ under Bernoulli disorder [ST03]. For the Ising perceptron, much less has been proved. One can introduce a parameter β ě 0 and de ne the associated positive-temperature partition function Z κ,β (see (7) below). e replica calculation extends to a prediction [GD88, KM89] for the limit of N´1 ln Z κ,β as N Ò 8 with M {N Ñ α. is formula has been proved to be correct at su ciently high temperature (small β) under Bernoulli disorder [Tal00]. For the original model (1), corresponding to zero temperature or β " 8, the best rigorous result to date is that for κ " 0 there exists positive γ such that γ ď M N {N ď 1´γ with high probability [KR98, Tal99] as N Ò 8 (see also [Sto13] for some work on general κ). Our m...