IF WW III Starts—we better not lose. Defeat would be a bitter pill to swallow and would stimulate a Civil War as people will seek scapegoats to blame the defeat upon. Just as the South blamed (unfairly) Blacks for their loss to the Yankees, liberal, environmentalists, Gay will be targeted and oppressed. Americans will not accept a loss and seek someone to blame like Germans after WW I blamed Jews and Communists for the “stab in the Back” (once again unfairly blamed).
I agree with your general premise that if the US were left intact after losing a war to Russia, a search for scapegoats would begin.
I come from a military family and coincidentally lived most of my life in the South. I would respectfully tend to disagree with saying Blacks were blamed for their loss in the War Between the States. I heard Jefferson Davis blamed a lot, and rich plantation owners for starting it and not serving in it, but not Blacks.