Black-hole-galaxy scaling relations provide information about the coevolution of supermassive black holes and their host galaxies. We compare the black-hole mass-circular-velocity (M-BH-V-c) relation with the black-holemass-bulge-stellar-velocity-dispersion (M-BH-sigma()) relation to see whether the scaling relations can passively emerge from a large number of mergers or require a physical mechanism, such as feedback from an active nucleus. We present Very Large Array HI observations of five galaxies, including three water megamaser galaxies, to measure the circular velocity. Using 22 galaxies with dynamical M-BH measurements and V-c measurements extending to large radius, our best-fit M-BH-V-c relation, logMBH = alpha +beta log(V-c/200 km s(-1)), yields a = 7.43+0.13 -0.13, beta = 3.68(-1.20)(+1.23), and an intrinsic scatter is an element of(int) = 0.51(-0.09)(+0.11). The intrinsic scatter may well be higher than 0.51, as we take great care to ascribe conservatively large observational errors. We find comparable scatter in the M-BH-sigma() relations, is an element of(int) = 0.48(-0.08)(+0.10), while pure merging scenarios would likely result in a tighter scaling with the dark halo (as traced by V-c) properties rather than the baryonic (sigma()) properties. Instead, feedback from the active nucleus may act on bulge scales to tighten the M-BH-sigma() relation with respect to the M-BH-V-c relation, as observed.