  Nearly every star known to host planets will become a white dwarf, and nearly
100 planet-hosts are now known to be accompanied by binary stellar companions.
Here, we determine how a binary companion triggers instability in otherwise
unconditionally stable single-star two-planet systems during the giant branch
and white dwarf phases of the planet host. We perform about 700 full-lifetime
(14 Gyr) simulations with A0 and F0 primary stars and secondary K2 companions,
and identify the critical binary distance within which instability is triggered
at any point during stellar evolution. We estimate this distance to be about
seven times the outer planet separation, for circular binaries. Our results
help characterize the fates of planetary systems, and in particular which ones
might yield architectures that are conducive to generating observable heavy
metal pollution in white dwarf atmospheres.
