Demonstrators gather in front of the U.S. Supreme Court for the "Not My Boss's Business" rally for women's health and rights in Washington

Religious rights versus women's rights. That's about as fundamental a clash as you can get in U.S. politics. It's now at the core of the 2014 election campaign, with both parties girding for battle.

What generated the showdown was last week's U.S. Supreme Court decision in the Hobby Lobby case. The decision instantly became a rallying cry for activists on both the right and left. Congressional Democrats are already proposing a law to nullify the decision. “It's shameful that a woman's access to contraception is even up for debate in 2014,” Senator Kay Hagan (D-N.C.) said.   Conservative blogger Erick Erickson crowed, “My religion trumps your ‘right’ to employer-subsidized, consequence-free sex.”

How did the issue become so big so fast? Because it touches some extremely sensitive nerves in the body politic.

Members of the Presbyterian Church of the Big Wood attend a service in Ketchum, IdahoThe question that best predicts a person's politics today is not about income or education. It's religion: How often do you go to church? Regular churchgoers -- including fundamentalist Protestants, observant Catholics, even many Orthodox Jews -- vote Republican. Voters who rarely or never go to church vote Democratic.

President Ronald Reagan brought the religious right into the Republican coalition. The Reagan coalition is the Old America -- and religious rights are a touchstone issue.