[en] Dissipative trapped particle modes are studied in tandem mirrors by including electron collisions and ion Landau damping. A variational approach is used to obtain a collisional response in terms of the collisionless result plus a collisional term. The collisional term is then self-consistently solved in all collision frequency regimes. One finds that when nu/ω << 1, (nu identically equal electron collision frequency) and the dissipationless theory is stable through a positive (negative) charge uncovering mechanism, there are two stable waves with phase velocities in the ion (electron) diamagnetic direction. The higher frequency wave with ω approx. ω/sub i/*(ω/sub e/*) is destabilized by ion (electron) dissipation while the lower frequency wave is destabilized by electron (ion) dissipation. At high collision frequency (nu > ω/sub e/*), the only unstable trapped particle wave has ω approx. ω/sub e/*, with electron collisions being destabilizing