Commiefornia - Cali, Washing State, Oregon, maybe Colorado, possibly parts of AZ and NM depending on if people leave before it goes down, parts of Idaho
Texlahoana - Texas, Oklahoma, Louisiana, maybe Arkansas
The SOUTH - Bama, Georgia, Mississippi, maybe SC too
Floridamanland - Florida is diverse enough and weird enough it might survive alone
The Commie South - Virginia, NC, eastern Tennessee
Ohio Basin - Ohio, Kentucky, Western Tennesee
Damned Yankee Land - You know where...except oddly enough probably excluding upstate NY and Maine
Leave us alone - ND, SD, Montana, Wyoming, Kansas, maybe Iowa
Chicagoland - Loosely affiliated city-states of Madison, Chicago, and Milwaukee
Mormon Paradise - Utah, southern Idaho
Vegas - Autonomous, Reno erects a wall around itself like Berlin to keep out the Californians
Missouri would most likely be its own state, given that they hate Kansas but really share nothing in common with anyone else in the area
But that's like some idealized RPG Balkanization...realistically, everyone in the rural areas walls off the liberal cities and it's Escape from NY, but replace NY with every large city run by Democrats.
"Peacefully"...the only way I can see that happening is if so many people die from a blight or something catastrophic (LOL @ Corona) that they're forced to become more self-reliant and the population contracts so much interstate trade becomes somewhat stagnant.
I do not want Boogaloo.
Neither did George Washington, but sometimes you just gotta do what you gotta do. Make sure you at least have a Hawaiian shirt on hand just in case.