Are we a Christian nation?

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I hear often that we are a Christian nation with Christian values. While I don't agree with that characterization, I'm not sure how others justify it.  I saw this quote from Colbert and found it really fitting and would love to hear explanations.  He said:
"If this is going to be a Christian nation that doesn't help the poor, either we have to pretend that Jesus was just as selfish as we are, or we've got to acknowledge that he commanded is to love the poor and serve the needy without condition and then admit that we just don't want to do it."
This is not an attack on Christianity and I'm sorry if you take offense. That is not my intention. I would like to understand what I feel is a misalignment of values in this country.