One pole.  Photographer: Saul Loeb/AFP/Getty Images
One pole.  Photographer: Saul Loeb/AFP/Getty Images

Abortion and guns, two of the most divisive issues in American politics, weren't always the stuff of partisan warfare. As it happens, they became more divisive, and more partisan, over roughly the same period -- the past 40 years. And it wasn't all happenstance -- a bit of planning went into it.

Let's start with abortion. Here is a list of prominent pro-life politicians of the past half century: Ted Kennedy, Al Gore, Richard Gephardt and Dennis Kucinich. Did I say "pro-life?" I meant, of course, "pro-choice." That's where each ended up after taking remarkably similar spiritual journeys -- through Democratic primaries.

Don't be too hard on those wobbly Democrats, though. Republicans proved just as shifty. One of the nation's most liberal abortion laws, pre-Roe v Wade, was signed in 1967 by California Governor Ronald Reagan. It expanded legal abortions to cases of rape, incest and, in a vast loophole that pro-lifers detested when it reappeared in the Roe decision, pregnancies that endangered a mother's "physical or mental health."

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At the time, Reagan's liberalization was in sync with his party and the nation. According to a 1972 Gallup Poll, 68 percent of Republicans agreed "the decision to have an abortion should be left solely to a woman and her doctor." (Democrats, who were more Catholic, were less supportive, with 59 percent agreeing.)

Yet Reagan soon had a conversion experience of his own, with -- what do you know? -- a Republican presidential primary in 1976 providing the impetus. In the years after the California law passed, Protestant evangelicals, who had never made much of a fuss about it before, made opposition to abortion a defining issue. At the same time, they claimed prime real estate in the Republican coalition. Feminists followed suit, only in reverse, embracing abortion as a fundamental right of womanhood and using their position in the Democratic coalition to demand the fealty of Kennedy, Gore, Gephardt and their ilk.

What happened?

A short answer is Richard Nixon. Elected in 1968 with a shaky 43 percent plurality, Nixon needed to enlarge his electoral coalition. He targeted Catholics, offering symbolic and substantive disapproval of abortion and a complement of public support for parochial schools. A longer answer is that after Nixon began courting anti-abortion social conservatives, the parties began sorting into distinct pro-life and pro-choice camps. In "Party Position Change in American Politics," from which many facts here are taken, political scientist David Karol wrote:

The parties' coalitions have changed and as a result senators are more responsive to the intense preferences of factions prominent in their party than to public opinion in their states where abortion is concerned.

As evidence of the political scramble on abortion, Karol makes this striking point: "Remarkably, until 2008 there was never a presidential race between two major party nominees who had taken consistent positions on abortion throughout their careers." (In 2012, Republicans reverted to form, nominating the sorta-pro-life, then pro-choice, then really-pro-life Mitt Romney.)

Via a combination of adaptation and replacement the parties' political elites became more polarized on the issue, a fact that encouraged activists on each side of the controversy to join the appropriate party," Karol wrote. "Once inside the party they reinforced its new position, producing further polarization and forestalling backsliding.

A similar process is evident on guns. Libertarians have tried to present an ideologically consistent front on guns and abortion, arguing for individual liberty over state regulation in both cases. In the 1980s, a liberal Catholic movement around Cardinal Joseph Bernardin of Chicago sought to make a "seamless garment" of pro-life views, opposing abortion, capital punishment, nuclear war and other perceived devaluations of life.

Neither attempt at ideological consistency found a home among Democrats or Republicans. "Ideologies are not clean world views derived straightforwardly from first principles," the political scientist Hans Noel told me in an e-mail. "They are pastiches of multiple, overlapping values, principles and gut feelings."

Gun rights used to be a mixed political bag, with positions drifting across party lines. As president, Nixon sought a ban on the cheap handguns known as "Saturday night specials." Liberal Democrat Eugene McCarthy, meanwhile, responded to the assassinations of 1968 by cautioning against passing gun regulation "under panic conditions."

That heterodoxy began to change as Republicans replaced Democrats in rural and Southern districts. In 1977, a coup at the National Rifle Association convention in Cincinnati accelerated the process, putting ideological hardliners in charge. In 1980, the NRA endorsed a presidential candidate for the first time -- Reagan. It subsequently became a powerful Republican constituency, helping to divide the parties on guns and then helping to cement those divisions in place.

The result? "Democrats from any region are now more supportive of gun control than Republicans from any region," wrote Karol. "As in the case of abortion, party affiliation has come to guide senators' positions more than views of their constituents."

Constituents, likewise, are influenced by the parties to which they gravitate. In effect, you may think you're a Democrat because you support gun control, or a Republican because you're pro-life, but it's just as likely that you value those respective issue positions precisely because your party does. Abortion and guns are both "now integrated into the larger ideological division," wrote Noel in an e-mail, "and the ideological division has a life of its own."

To contact the writer of this article: Francis Wilkinson at fwilkinson1@bloomberg.net.

To contact the editor responsible for this article: Tobin Harshaw at tharshaw@bloomberg.net.