Are we a Christian nation?

From a 2007 poll, 

Sixty-five percent of Americans believe that the nation's founders intended the U.S. to be a Christian nation and 55% believe that the Constitution establishes a Christian nation.

From President Obama's address to the Turkish press today:

I've said before that one of the great strengths of the United States is, although as I mentioned we have a very large Christian population, we do not consider ourselves a Christian nation or a Jewish nation or a Muslim nation. We consider ourselves a nation of citizens who are bound by ideals and a set of values.

I applaud the sentiment, Mr. President, but I'm not sure who this "we" is you're talking about.