When people hear the words Christian Nation one assumes that one is in favor of some sort of return to Constantine like rule. Or some sort of Christen Equivalent of The Middles East's Sharia Law. However, nothing could be further from such a thing. Sharia Law is a top down and authoritarian worldview, Islam is a doctrine of demons which pushes Jihad and violent overthrow/enforcement of that doctrine on all people. The reform of the Nations to God's Law is a bottom up and gradual view.
A Christian Nation comes about as God Saves people and they Disciple the Nations from the ground up. One does not wish to force the Nation to be Christian, but, get voted in by the people within it. Only when The Nations vote in people with a Christian Worldview will the Nation come to be. We also can and should aim for a gradual change towards the end goal. Just as we have wavered away from even a shred of Christendom we can waver back.
In the meantime we can support as many God Honoring decisions by those we vote for as we can find. The end goal is to get as much of a Christianity influenced government as possible. However, a Fully Christian Nation might not come about given how Revelation talks about the future. That does not mean The Lord is not on his Throne Ruling and Governing as we speak. As He sure is and will continue to do so until His Second Coming when all will be made new.