Are people forgetting that the USSR lent support to North Korea and China lent support to North Vietnam-- at times when both those countries were nuclear powers? It has been demonstrated several times throughout the past 70 years that nuclear nations can be brought into conflict (however indirectly) without resorting to using WMDs.
PTSD from Bush's wars has completely fried the brains of most Americans, it seems. Anything involving the military doing its job, even if it doesn't involve violence, is seen as "endless war" or whatever other buzzword politicians have been throwing around the get elected. In reality, there is no contradiction between thinking that the Iraq war was an abomination and also thinking that we need a defensive show of force to make sure Putin stops at Ukraine.