WASHINGTON — In the 1980s, President Ronald Reagan instructed Haley Barbour — his White House political director and a future Republican Party chairman and governor — on building a winning coalition: “The person who agrees with you 80 percent of the time is a friend and an ally — not a 20 percent traitor.” By practicing what he preached, the Gipper carried 44 states the first time he ran and 49 states the second while helping create a new electoral group, Reagan Democrats.

A successful political party is not some exclusive social club with its own admissions test that people must pass to be accepted. No, a successful political party is, by definition, a coalition of different people who come together to work to win elections in order to enact policies on which they mostly agree. The first major event in opposition to the brand-new Trump administration, the Women’s March on Washington, imposed a litmus test and officially excluded the 46 percent of Americans (including 43 percent of women) who, when asked by the Gallup Poll about the issue of abortion, identified themselves as “pro-life” rather than “pro-choice.” For the record, 47 percent in the same survey self-identified as “pro-choice.”

The event was co-sponsored by Planned Parenthood and NARAL Pro-Choice America, and its organizers made clear that — regardless of a group’s demonstrated commitment to the need for universal child care, equal pay for equal work, the rights of immigrants, gays, lesbians and ethnic and religious minorities, and fighting poverty — no pro-life group would be welcome: “The Women’s March’s platform is pro-choice and that has been our stance from day one.” Any so-called “anti-choice” group could not be “a partner of the Women’s March.” Organizers made clear that only one issue mattered: unquestioning belief that abortions should be legal under any circumstances. That position is supported, according to Gallup, by just 29 percent of Americans, while 7 in 10 believe abortion should be either “illegal in all circumstances” (19 percent) or “legal only under certain circumstances” (50 percent).

Abortion continues, as it has for the 44 years since the Supreme Court decision that legalized it as an unrestricted right for a woman in the first trimester of her pregnancy but ruled that the state has an interest, after that, in protecting what Hillary Clinton — causing herself considerable grief with some liberal supporters — publicly referred to as an “unborn person.” Clinton — who, after securing the Democratic presidential nomination last year, celebrated her victory by going to Planned Parenthood and had the all-out support of pro-choice groups — upset some ardent supporters by declaring on national television that “of course you can be a feminist and be pro-life.”

Americans are dramatically more liberal and accepting today than we have ever been on the moral acceptability of gay and lesbian relations and same-sex marriage. And by a lopsided 15-1 margin, birth control — once a thorny issue — is now judged to be morally acceptable. But abortion is different. In 2001, in the first year of George W. Bush’s presidency, 42 percent of us told Gallup that abortion is “morally acceptable,” and 45 percent called abortion “morally wrong.”

In the last year of Barack Obama’s presidency, the percentages were similar. Forty-three percent answered “morally acceptable” on abortion, and 47 percent responded “morally wrong.” Ambivalence on this painful matter endures; Americans are simultaneously both pro-choice and anti-abortion.

You can almost always gauge the health, as well as predict the success or failure, of any political movement by whether that movement is seeking and welcoming converts to its cause or whether instead it is hunting down and banishing heretics from its ranks. By rejecting people Ronald Reagan would have called liberals’ valuable and committed allies just because they do not toe the pro-choice line, the Women’s March on Washington’s leadership flunked that basic test.

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To find out more about Mark Shields and read his past columns, visit the Creators Syndicate webpage at www.creators.com.