Experts debate at OpposingViews.com:

In a 2007 interview with beliefnet.com, John McCain stated that “the Constitution established the United States of America as a Christian nation.” While some were encouraged by McCain’s words, others took great offense, reigniting a passionate debate about the intentions of America’s founders. Was the U.S. built on Christian principles, or are we a purely secular nation?

Read arguments from both sides here.