If at first you don’t secede, try, try again!
You guys have it all wrong, its not secession but expulsion, take Illinois for example, the entire state is a red state except for Cook county. What you do is have a private meeting of all State Senators except those from Cook County and they vote to exclude Cook County from the State. Then all the State Reps meet and do the same. Now the State Government of Illinois is reconstituted both houses impeach the Governor and elect a new one pending general elections. Done. Illinois except for Cook county is reconstituted without the offending county which is on its own. The State is solidly red and now treats Cook County as a foreign or separate state.
States where there is a red region that is dominated by the rest of the state could do the same but that would be state secession and there should be red states nearby to offer assistance. And finally the US could also do it, with the Red House members voting to expulse the handful of Blue States from the Union. Then the Senate without those Blue States’ Senators convenes and votes on the expulsion. Done. The house impeaches the president and the Senate ratifies it. Given the exceptional circumstance the Senate elects an Interim President and the House ratifies it. Expulsion is much better than secession because you are protecting the institutions not replacing them. Secession should only be used where a state is purple with a large red area. The point is to keep as much of the US intact as possible.
Secession would be key in a location such as Western NY where the Niagara Power Authority is. Also parts of California are red and that would give the Red US access to the Pacific. What the Blue states would do in such an event would be open to conjecture, I am sure they would be unhappy about it.
Remember that with expulsion their unstable governments and burgeoning populations would quickly render them disaster areas. Also remember that except for the Navy most military instillations are in Red States. Food for thought.