The "born-again" America was not always so religiously-oriented. Perhaps you already know, but our money only started saying "In God We Trust" in 1956, and "under God" was added to the pledge of allegiance around the same. The Cold War was the impetus for a lot of the surge in the return to Christianity we have been experiencing. It was largely a reactionary fear of the state-atheism of the Soviet communists. America greatly feared the possibility of Soviet infiltration and that meant that whatever Soviets claimed to be was what we hated most.

The anti-communist frenzy continued and witch hunts for atheists, as well as homosexuals, leftists, hippies, and any other group allegedly aligned with communism raged for quite a while, often at the behest of the ambiguously sexual J. Edgar Hoover's FBI. The first "born again" president of the US was actually Jimmy Carter, who was kind of a symbol that yes, revivalist Christianity was back in the mainstream.

Since the 40's, the Republican party, which originally consisted of fiscal conservatives primarily, started associating and joining forces with with social conservatives, who often included devoutly religious folks. One of the biggest, and most influential detractors from FDR was Father Coughlin, a Catholic priest and arguably the grandaddy of televangelists, with the first wide-spread religious radio show. (unfortunately, Coughlin had a bad tendency of agreeing with policies set out by Mussolini and Hitler but that's besides the point).

Ever since FDR, the Right wing of the government has been the holy union of fiscal conservatives with mostly religious social conservatives. This has led to a national party of "common sense" and tradition which has pervaded deep into our culture and the two now seem inseparable (although the growing popularity of the Libertarian party, especially among the youth who are disappointed with the Democrats should give the right pause).

All of this has led to a situation in America where minimally half of the choices available to us in leaders are not just open with their religion but tout their faith as though it were enough for them to claim a right to political office. Questioning the faith of leaders is seen as taboo, and merely making a statement of irreligion is seen as offensive (if you need a reminder, how about the bus ads that merely said "ATHEISM" which were deemed too offensive to run?) When we feel we are at war (as we are, allegedly, with the broad concept of terrorism and with the somewhat narrower group, radical Islam) fear tends to bind our culture into something resembling unification. That means that, whether it makes sense or not, patriotism is being aligned with God because 55 years ago, we decided that God had a place in allegiance to our nation.

That's sort of an abbreviated version of how we got here in the last half-century or so. I hope it begins to answer your question. Understand that there is a lot to be said for the power of community and fear for keeping religion a dominant social force.