Roe v. Wade. Sometimes those seem like the most contentious words in American law. Short and unassuming though they are, they connote other, more explosive terms: abortion and murder, morality and privacy, the right to life and the right to choose. Attached to those words are some of the most intractable passions in American life. Writing about medical advances that improve the chances for a fetus to survive outside the womb, U.S. Supreme Court Justice Sandra Day O’Connor once declared that the 1973 decision was “on a collision course with itself.” Sixteen years after Roe obliged all 50 states to legalize abortion, the nation is on a political collision course. This week a Supreme Court refashioned by Ronald Reagan will hear arguments in William L. Webster v. Reproductive Health Services, a case that could lead to Roe’s being seriously weakened or even reversed. Either outcome would mean a new world, one in which abortions could be banned in many states or made greatly more difficult to get. After years in which court dictates let politicians dodge the whole roiling issue, abortion would be forced back into the political arena. Back to state legislatures and referenda. Back to lawmakers and voters. Back to the streets too, where it is already being disputed more fiercely than ever. The pro-life advance guard is now represented by the shock troops of Operation Rescue chaining themselves to the doorways of abortion clinics. And when more than 300,000 abortion-rights marchers poured through the streets of Washington a few weeks ago, it was clear that the threat to Roe has jolted the desultory pro-choice movement back to life. “You can’t expect it to remain peaceful in these circumstances,” says Ruth Pakaluk, president of Massachusetts Citizens for Life. “It’s like the Civil War. There is no suitable middle ground.” Yet an uneasy middle ground is precisely the territory that many Americans occupy. Pollsters commonly find that about 40% of the public believe abortion should be available for any reason a woman may choose. A slightly higher percentage typically believe it should be available only in cases of rape, incest or to protect the health of the mother. But a large majority, usually around 70%, regularly say the decision to have an abortion should be left to the woman. A poll conducted April 4-5 for TIME and CNN by Yankelovich Clancy Shulman produced similar results. While half of those questioned believe abortion is wrong, 67% favor leaving the decision to a woman and her doctor. Fifty-four percent still support the Roe decision, and 62% oppose limiting a woman’s right to have an abortion during the first three months of pregnancy. In effect, most Americans would treat abortion as something like divorce — an anguishing decision but not a crime. Pro-life forces want to convince them that abortion is more like murder — one of those acts that cannot be sanctioned as a choice. As each side flourishes its arguments and passions, its pictures of fetuses and coat hangers, the conscience too can feel set on a collision course with itself.