  We investigate how cosmic rays (CRs) affect thermal and hydrostatic stability
of circumgalactic (CGM) gas, in simulations with both CR streaming and
diffusion. Local thermal instability can be suppressed by CR-driven entropy
mode propagation, in accordance with previous analytic work. However, there is
only a narrow parameter regime where this operates, before CRs overheat the
background gas. As mass dropout from thermal instability causes the background
density and hence plasma $\beta \equiv P_g/P_B$ to fall, the CGM becomes
globally unstable. At the cool disk to hot halo interface, a sharp drop in
density boosts Alfven speeds and CR gradients, driving a transition from
diffusive to streaming transport. CR forces and heating strengthen, while
countervailing gravitational forces and radiative cooling weaken, resulting in
a loss of both hydrostatic and thermal equilibrium. In lower $\beta$ halos, CR
heating drives a hot, single-phase diffuse wind with velocities $v \propto
(t_\mathrm{heat}/t_\mathrm{ff})^{-1}$, which exceeds the escape velocity when
$t_\mathrm{heat}/t_\mathrm{ff} \lesssim 0.4$. In higher $\beta$ halos, CR
forces drive multi-phase winds with cool, dense fountain flows and significant
turbulence. These flows are CR dominated due to "trapping" of CRs by weak
transverse B-fields, and have the highest mass loading factors. Thus, local
thermal instability can result in winds or fountain flows where either the heat
or momentum input of CRs dominates.
