  Using a three-dimensional quasiclassical technique we explore molecular
double ionization by a linearly polarized, infrared (800~nm) 27~fs laser pulse.
For intensities ranging from the tunneling to the over-the-barrier regime, we
identify the double ionization pathways in a unified way as a function of total
electron energy. For the tunneling regime, we discuss the differences in the
interplay of double ionization (DI) pathways between strongly driven He and
strongly driven $N_{2}$. For intermediate intensities in the over-the-barrier
regime, we find that both the correlated momenta and the double ionization
probability distribution as a function of total energy probe the tunneling
phase of the re-colliding electron. This allows for a direct verification of
the re-colliding electron tunneling at a large phase of the laser field in the
over-the-barrier regime in contrast to a small tunneling phase in the tunneling
regime.
