McQuilkin and Copan argue that attempts to return to a Christian America are in danger of becoming idolatrous because of

Their reliance on a political majority

Explanation:

McQuilkin and Copan actually argues that attempts to return to a Christian America are in danger of becoming idolatrous because of their reliance on a political majority.

McQuilkin and Copan shows that there is the danger of the Christian America to become idolatrous. Such danger is to be attributed to their reliance on the majority of the political people available.

McQuilkin and Copan focuses on how believers fulfil God's purpose for their lives.