It was recently shown that the exact factorization of the electron-nuclear
wavefunction allows the construction of a Schr\"odinger equation for the
electronic system, in which the potential contains exactly the effect of
coupling to the nuclear degrees of freedom and any external fields. Here we
study the exact potential acting on the electron in charge-resonance enhanced
ionization in a model one-dimensional H2+ molecule. We show there can be
significant differences between the exact potential and that used in the
traditional quasistatic analyses, arising from non-adiabatic coupling to the
nuclear system, and that these are crucial to include for accurate simulations
of time-resolved ionization dynamics and predictions of the ionization yield
