Two methods measure the present expansion rate of the universe and they do not agree. The cosmic microwave background, interpreted through the standard cosmological model, yields a Hubble constant of 67.4 km/s/Mpc; the local distance ladder, built from Cepheid-cali- brated Type Ia supernovae, yields 73.0 km/s/Mpc. The gap has hardened from a curiosity into a roughly 5σ discrepancy that no amount of additional data has dissolved. This article asks a delib- erately narrow version of the broad question: could the discrepancy be an artifact of systematic error in the calibration of Type Ia supernovae as standard candles? Standard error analysis an- swers this by estimating each systematic, propagating it forward, and reporting a total uncertainty — a procedure that, by construction, cannot tell us whether the systematics are large enough to matter. This article introduces a different procedure. I propose inverse systematic-error budget- ing: rather than propagating errors forward, the method starts from the observed tension and computes, for each candidate calibration systematic, the magnitude it would need to have in order to fully close the gap — its closure requirement — and then tests that requirement against the magnitude the data actually permit — its empirical envelope. A systematic qualifies as a viable closure candidate only when its closure requirement falls inside its empirical envelope. Applying the method to eight identified Cepheid and supernova systematics, drawing on seventeen Scopus- indexed studies and seven institutional sources, produces a clear result: the tension demands a coherent offset of approximately 0.17 magnitudes in the distance-ladder zero-point, while no individual systematic has an empirical envelope exceeding 0.06 magnitudes, and the envelopes summed in quadrature reach only 0.11 magnitudes. No single calibration error can close the ten- sion; only an implausible same-sign alignment of all eight systematics at their extreme permitted values could do so. The host-galaxy dust-law degeneracy emerges as the systematic with the wid- est envelope and therefore the highest residual closure viability, identifying it as the priority target for further observational constraint.