In a practical way, America didn't start as a Christian nation and I really don't write that to be controversial. I'm sure it is controversial to some. In recent decades, David Barton in addition to several others has written or posted much material documenting America as a Christian nation. The founding fathers didn't intend, however, to start a theocracy per se, where the Bible was a founding document. Since the nation was a democratic republic dependent on self-government, Christianity impacted the decision making through its people. Alexis de Tocqueville made that point in his classic book, Democracy in America.
Idealogically, I think an argument could be made that America was at one time a Christian nation. The second paragraph and main body of the Declaration of Independence, the founding document of the United States begins:
We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights.
You read the words, "self-evident" (natural revelation), "created," and "endowed by their Creator." Notice that it also reads, "these truths," not facts or ideas or concepts. "Truths" means absolutes because there are absolutes and that's what they believed. All of these are Christian language derived from a Christian view of the world, which could be only the Christian God, which is the only God.
When you read Noah Webster's 1828 Dictionary was titled, American Dictionary of the English Language. Webster published the first American dictionary, which uses verses from the New Testament for examples of the words therein. The original American colleges, the Ivy League ones, were Christian. Many quotes from founding fathers, including from James Madison, Father of the U. S. Constitution, say that idealogically the United States started Christian.
One can argue this point either way. I see America one time as a Christian nation. If that is the case, then how did things change? A majority of Americans no longer see America as a Christian nation.
Christianity is Christianity. Something called Christianity that isn't even Christian any more can't be counted as Christianity. What was Christianity when America was Christian isn't even what Christianity is today. America can't be Christian because of something called Christianity, but because of something that is Christian.
Early colleges started because of and for Christianity. They were Christian. Now Christianity isn't welcome in America's colleges and universities. The Declaration starts with Creator and Creator isn't welcome in America's institutions. Just the opposite, Christianity is attacked there.
At one time, businesses closed on the Lord's Day. Now Sunday is one of the most worldly days of the week in America. Sunday is a good day for travel and recreation. The thought of church barely enters into society. America hasn't stopped us from talking about Christianity, but it's not a sure thing that it is legal to live it any more.
Politicians still use their Christianity for votes. It's still worth something, but it won't win an election. It won't lose an election unless you attempt to use it in a phony way. If you think you have a Christian candidate, don't think we will return to a Christian nation again because of him. You need to become accustomed to Christianity in a secular state, a place where Christianity in general is not welcome. I like to think of it as being a missionary to France. It's not that bad, but it's that to which you should become prepared. The people of France don't expect a Christian president.
Enjoy your church. Have a Christian church. Have a Christian family. Don't expect a Christian nation. It will be a waste of time for you.