I would disagree that the US is a Christian country. Yes, it is the majority by a long shot. But lets get a few things straight.

I hesistate to say "the majority", but a substantial amount of people do not go to church on a regular basis. This includes believers. And while one does not have to attend church to believe, I bring this up because a substantial number of "believers" also do not adhere to the lifestyle. It's called being a "convenient christian." Ask a man convicted of rape and murder what his religion is...most likley christian. Go to a strip club with an anti-christian slogan on your shirt and expect to get punched by a "christian." Having "christian beliefs" does not make one a religious person, the funny thing being that most "christian beliefs" adhere to the same core principles as just about every other religion.

We are secular, which means that religion affects, at most, laws and legislation indirectly, so much that even in-your-face christians will often cringe when a loon tries to justify some crazy knee-jerk law based on "Gods will." Yeah, yeah, this on time Bush said that one thing about God guiding him blah blah. That's what that is, it's blah.

To be honest, I am very comfortable where we are as a country in terms of religion. It is here, but it is not. Yes, a christian candidate will likley have leverage over a non-christian, but that honestly does not bother me because most christian politicians -- even the religious conservative ones -- don't legislate through the Bible. There is a large segment of the political conservative movement who holds animosity towards the religous right for highjacking the GOP because GOP fiscal and social intervention principles are incompatible with GOP Christian nanny-state ideas no matter how you boil it down.

The only reason more non-believer leaders haven't come out as such is because they have a better chance of winning if they "believe." Photos of a president coming out of church holding a bible goes an awful long way with Granny.

The American left, Eurpoean press and muslim nations try fairly often to paint America as some big, Christian doom machine, when in fact we are so sectarian that trying to post the 10 commandments in a court house brings out the alligators and people lost jobs and re-elections.

to the OP:
My answer is no, religion is not necessary, and I think that you will find the majority of americans feel the same way