how exactly is "the foundation of our Constitution . . . based upon the Bible"?

It's not. In fact, the Founding Fathers made statements to the contrary. There was a treaty which read that in no way was the Constitution based upon the Christian religion.

The Mayflower Compact, the founding theoretical document of the Massachusetts colony was based on the bible. This legal tradition lasted several generations and then gave way to our secular legal foundation- the US Constitution. The Constitution's philosophical and legal theory arose from the Enlightenment which was heartily condemned has heretical by Christianity.

It's not. The founding fathers didn't want an official state religion, since there were already different religious groups in the US- Quakers, Protestants, etc.

It is clearly not. Doesn't even contain the word "God" in it anywhere.

The concepts our constitution is based on come more from John Locke, an English Philosopher.

Simple. It's not. Nowhere in the constitution will you find the word God, Jesus, Holy, Bible, Christ, Christian, Scripture etc.

Yes, It was a convenient way for politicians to control people.