Don't forget, many in the military are liberals. Also, it isn't difficult to learn to shoot a gun. Any civil war that is 50-50 population wise will be close, and don't forget, things like economy and allies matter. A state like California, which is liberal, has the sixth largest economy in the world. This would allow them to produce guns at an extraordinary rate, not to mention tech giants are based there. Europe would most likely align with the liberals while Russia may decide to aid the conservatives. It is also worthy to note that liberals overwhelmingly out-populate conservatives when it comes to colleges and the tech giants too. More innovative technology is likely to come out of the liberal side than the conservative (this is not an opinion, but a statement based on trends). It would be close, let's hope it never happens!
Note: I am neither liberal nor republican, but independent.