In their unflagging efforts to distance themselves from mainstream America, Republican leaders have gleefully seized upon a social issue that’s guaranteed to backfire in November:

Birth control.

If you’re mystified, you’re not alone. Ignoring years of public-opinion polls, the GOP is boldly marching backwards into the 1960s to question whether contraception is a legitimate health-care benefit.

The target, as always, is President Obama. He issued an executive mandate requiring that free birth control be included in health plans provided to employees of schools, charities and hospitals connected to religiously affiliated institutions.

Although the mandate excludes churches, Roman Catholic bishops are in a huff, saying the contraception provision violates the First Amendment and “freedom of religion.”

Never mind that Obama softened the rule so that the insurance companies, not the employers, will pay for the coverage. Never mind that many employees served by these healthcare plans don’t share the same religion as the institute for whom they work.

Republican strategists see the controversy as another opportunity to bash Obama’s healthcare reforms, and also to rile up white Christian evangelicals who don’t like the president anyway.

As political miscalculations go, this one could be epic. If you’re looking for a sure way to galvanize female voters against your own party, attack birth control.

Whom does the administration’s mandate help? Teachers, secretaries, nurses, lab techs — working women who can’t afford, or don’t choose, to get pregnant.

Yet to hear the yowls of outrage, you’d think these hospitals and schools were being ordered to round up their workers and force-feed them birth-control pills against their will.

Leading the opposition are Catholic bishops, whose archaic dictums against contraception are widely disregarded by their own flock. According to most surveys, about 98 percent of sexually active Catholic women use some type of birth control.

It’s safe to assume that rather large segment includes employees of, say, the University of Notre Dame.

Polling also shows that more than two-thirds of all practicing Catholics believe you can still be a good Catholic if you use contraception. So, they basically humor the church hierarchy on this subject, politely listening to priestly reminders and acknowledging the occasional admonition from the pope himself.

There’s no movement to excommunicate parishioners for the alleged sin of using condoms, IUDs or pills because that would effectively leave most churches empty as a tomb on Sundays.

Now, after decades of having their stance against birth control ignored, Catholic bishops have finally found a receptive audience: Republicans in Congress.

Last week, having nothing more important to do, a House committee scheduled a hearing modestly titled: “Has the Obama Administration Trampled on Freedom of Religion and Freedom of Conscience?”

Meanwhile, Senate Republicans are seeking to block any health-insurance rules that conflict with a business owner’s private beliefs, whatever that means. If such an amendment passes, we could theoretically see a mass conversion to Catholicism among company executives trying to squirm out of offering birth control in their employees’ medical policies.

Smart corporations already provide contraceptive coverage because it’s way cheaper than paying obstetrical costs for unplanned pregnancies.

Interestingly, as the bishops and their newfound evangelical allies promise to fight on in the courts and in Congress to knock down the president’s rule, little mention is being made of the large federal sums received by many of the religiously affiliated institutions affected by the birth-control mandate.

Why should any school or hospital that takes a dime of taxpayer money be exempt from providing the same healthcare benefits that apply across the board? That’s what contraception is — basic health care — and that’s how it’s perceived by a majority of Americans.

In a New York Times/CBS poll last week, 65 percent of those surveyed said they support Obama’s directive that all health-insurance plans should include birth control. Fifty-nine percent of everyone interviewed, as well as 57 percent of Catholics, said contraceptives should also be provided by the medical plans of religiously-affiliated employers.

Obviously, limiting the availability of birth control is an unpopular idea in this country. That it’s getting traction in Congress illustrates how completely the Republican Party has been carjacked by its bug-eyed, right-wing fringe.

Even as national women’s groups mobilize to support the administration, the GOP presidential candidates are piping up to denounce the birth-control benefit as a sinister plot against religion. Among the alarmed is Mitt Romney, who as governor of Massachusetts uttered not a whisper of objection to a state law that was virtually identical to the president’s mandate.

You can be certain that the fall election won’t hinge on social issues that were settled in the minds of voters decades ago. If the Republicans stay on this sorry, dead-end path, Obama’s task is clear:

Ice the champagne.