My thoughts were to separate the midwest/south contingent (or New Jerusalem – Capital would be either Lincoln or Topeka) from the more progressive states in the East and West.
The Eastern section (New America and they can keep DC as its Capitol) would begin at the border between North/South Dakota and Minnesota then East to the Mississippi River, down the Mississippi to the Tennessee/Kentucky border then East to the Atlantic Ocean.
On the West Side (Either Cascadia or LaLaLand, Capitol at Portland) begin Southward from Canada along the Washngton/Oregon border with Idaho then East at the Nevada border to Wyoming. South then East along the Wyoming/Colorado border to Nebraska then South along Colorado/New Mexico to Oklahoma then follow the New Mexico border to Mexico.
Not perfect by any means and Arizona/Utah might be a problem but we could just give those back to Mexico and let them worry about it. Oregon, Maine, NH and Vermont might choose to go with Canada and Montana/ North Dakota are kind of iffy. They might choose to go with the Great White North or to stay with the Eastern contingent but they have contiguous borders.with all so no big problem Hawaii would probably stay with the Cascadia/LalaLand portion while Alaska can do as it damn well pleases, no one really cares.