Many people claim that America is a Christian nation, but democracies cannot be religious in nature without discriminating against those of other faiths and philosophies. Jesus summarized the essence of his ethical teachings as being a good neighbor. Being a good neighbor begins with respecting others for who they are, and not using religion to dominate them.
If one claims that the founders of this nation were Christian, would that not also imply that enslaving African people and slaughtering the native people in order to steal their land was also Christian? Does no one notice that the myth of a Christian nation also provides a pretext for privileging those of European descent? After all, Christian conquerers are the heroes of that story, not the natives who were here first, not the enslaved people who had religions of their own, not the Jews and the Deists and the non-believers who were here as well. Can we really say that our non-Christian neighbors are irrelevant to our national story simply because there are more of us, and we can outshout them?
In a nation of many faiths and philosophies, being a good neighbor requires a secular state. If any would like to make America more Christian, they might begin by being better neighbors themselves.