Washington (CNN) -- What's the most emotional and divisive issue in American politics?





Abortion, right?





Just this weekend, former Republican front-runner Rick Perry used the abortion issue to slam current Republican front-runner Herman Cain at the Iowa Faith and Freedom forum.





Perry said:





"It is a liberal canard to say I am personally pro-life, but government should stay out of that decision. If that is your view, you are not pro-life, you are pro having-your-cake-and-eating-it-too."





Over the previous week, Herman Cain had alarmed anti-abortion voters with a series of verbal miscues, indicating both that abortion must be stopped but also that the decision should be left to the individual woman, with no role for government.





At the Faith and Freedom forum, Cain over-corrected for his week of stumbles: "No abortions. No exceptions." That new position goes far beyond the usual pro-life policy, which allows exceptions for rape, child abuse, and to save the life of the mother.





Pro-life activists must unhappily confront the probability that many of the leading candidates for the GOP nomination in 2012 - while all professedly pro-life - in reality neither care very much nor think very much about the abortion issue.





But now look at the world from the politicians' point of view. They must hold together a coalition that is sliced apart by the abortion issue. Pro-choice Republicans do not hold forums. But they exist, and they have power. With the result that while you can't get nominated for president by the GOP if you are pro-choice (see Giuliani, Rudy), you also can't get nominated if you oppose abortion too much (see Huckabee, Mike).





For the politicians, it's all baffling and vexing.





And yet -- incredible as it sounds now -- there is reason to expect that the abortion issue may someday just vanish from national politics. After all, that's what happened to the last great moral issue to rattle the American party system: alcohol prohibition.





For 70 years from the end of the Civil War to the Great Depression, a human lifetime, the "drys" and the "wets" mustered all the passion, commitment, and moralism of the pro-life and pro-choice movements of our day.





"It is my opinion that the saloonkeeper is worse than a thief and a murderer. The ordinary thief steals only your money, but the saloonkeeper steals your honor and your character. The ordinary murderer takes your life, but the saloonkeeper murders your soul."





That's from the famous "booze sermon" of Billy Sunday, the great popular preacher of the 1910s and 1920s. Thousands of such passionate speeches -- millions more passionate words -- were uttered by names now brown with history: William Jennings Bryan, Carrie Nation, Elizabeth Cady Stanton. It was not all talk. Ferocious legislative battles were bought to prohibit alcohol at the county, state and then ultimately national level. The great scholar of American politics, Judith Shklar, estimated to her graduate students that through the long run of American history, more elections at more levels of government have turned on alcohol than any other issue, including slavery.





Politicians hated the alcohol issue for the same reason they now dislike the abortion issue: It sliced apart the existing party structure.





The Republicans could not win a national majority without the support of Protestant immigrants from Germany in cities like Milwaukee and St. Louis. The Democrats could not win without the enthusiastic support of Irish Catholics in New York and New England. City-dwelling Germans and Irish intensely resented attempts of their country-dwelling neighbors to regulate their behavior for them.





"If they don't feel like takin' a glass of beer on Sunday, we must abstain," a contemporary Irish-American politician bitterly complained. "If they have not got any amusements up in their backwoods, we mustn't have none."





National politicians responded to Prohibition then in the same way
What did he say about abortion? What did Herman Cain say? Who is Herman Cain? What caused the tear of American politics?
must be stopped but also that the decision should be left to the individual woman, "No abortions. No exceptions." Republican front-runner Abortion,
question: What did he say about abortion?, answer: must be stopped but also that the decision should be left to the individual woman, | question: What did Herman Cain say?, answer: "No abortions. No exceptions." | question: Who is Herman Cain?, answer: Republican front-runner | question: What caused the tear of American politics?, answer: Abortion,