The solar active region photospheric magnetic field evolves rapidly during major eruptive events, suggesting appreciable feedback from the corona. Using high-cadence vector magnetogram sequence, multi-wavelength coronal imaging, and numerical simulation, I will show how the observed photospheric "magnetic imprints" can be used to estimate the impulse of the Lorentz force that accelerates the coronal mass ejection (CME) plasma. In an archetypical event, the Lorentz force correlates well with the CME acceleration, but the total force impulse surprisingly exceeds the CME momentum by almost two orders of magnitude. I propose a "gentle photospheric upwelling" scenario, where most of the Lorentz force is trapped in the lower atmosphere layer, counter-balanced by gravity of the upwelled mass. This unexpected effect dominates the momentum processes, but is negligible for the energy budget. I will discuss our follow-up project, how the upcoming high-sensitivity observations and new- generation numerical models may help elucidate the problem.