Here’s a story of utter irresponsibility: About one-third of American girls become pregnant as teenagers.

But it’s not just a story of heedless girls and boys who don’t take precautions. This is also a tale of national irresponsibility and political irresponsibility . of us as a country failing our kids by refusing to invest in comprehensive sex education and birth control because we, too, don’t plan ahead.

I kind of understand how a teenage couple stuffed with hormones and enveloped in each other’s arms could get carried away. But I’m just bewildered that American politicians, stuffed with sanctimony and enveloped in self-righteousness, don’t adequately invest at home or abroad in birth-control programs that would save the government money, chip away at poverty, reduce abortions and empower young people.

Neither Democrats nor Republicans seem particularly interested in these investments. The inflation-adjusted sum spent on Title X family planning in the United States has fallen by two-thirds since 1980.

A few depressing facts:. American teenagers become pregnant at a rate of about one a minute.

. Some 82 percent of births to teenagers in the U.S. are unplanned.

. American and European teenagers seem to be sexually active at roughly similar rates, although Americans may start a bit earlier. But the American teenage birthrate is three times Spain’s rate, five times France’s, and 15 times Switzerland’s.

. Young Americans show a lack of understanding of where babies come from. Among teenagers who unintentionally became pregnant, the Centers for Disease Control and Prevention found that the most cited reason for not using contraception was “I didn’t think I could become pregnant.” And 18 percent of young men somehow believed that having sex standing up helps prevent pregnancy, according to the National Campaign to Prevent Teen and Unplanned Pregnancy.

Hello?A teenager who has a baby often derails her own education and puts the child on a troubled trajectory as well. In Oklahoma last year, I met one family where the matriarch had a baby at 13, her daughter had a baby at 15, and that child, in turn, gave birth at 13. That’s how poverty replicates.

Medicaid spends an average of $12,770 for a birth. Yet we spend only $8 per teenage girl on programs to avoid pregnancy. In financial terms, that’s nuts. In human terms, it’s a tragedy.

Internationally, we and other donor countries also underinvest in family planning in poor countries. Globally, 220 million women don’t want to become pregnant but lack access to contraception.

Isabel Sawhill of the Brookings Institution has written an important new book, “Generation Unbound: Drifting Into Sex and Parenthood Without Marriage.” She notes that most young single moms in America don’t intend to become pregnant but drift into it fatalistically, partly because they rely solely on condoms or other less reliable forms of birth control.

Condoms are 82 percent effective in preventing pregnancy in any one year, according to the C.D.C. But that means that after four years of relying only on condoms, most women will have become pregnant at least once.

So Sawhill advocates a move to what she calls “childbearing by design, not by default.” That means providing long-acting reversible contraceptives, or LARCs, to at-risk girls and young women who want them. LARCs are IUDs, or implants that can remain in place for years, and the failure rate is negligible.

Teenage birthrates in America have already dropped by more than half since 1991. But Sawhill calculates that if LARCs became much more widespread, the proportion of children born outside marriage could drop by a quarter, and the proportion of children who are poor would drop sharply as well.

“By turning drifters into planners, we would not only help those women achieve their own goals but also create much stronger starts for their children,” Sawhill writes.

The American Academy of Pediatrics recently urged doctors to recommend LARCs for sexually active teenagers. One obstacle is the initial cost . $500 to $1,000 . so that many young people can’t afford them.

A study in St. Louis offered free birth control, including LARCs, to sexually active teenagers and found that pregnancy rates for them plunged by more than three-quarters. Abortions fell by a similar rate. That’s what we need nationwide.

The Affordable Care Act provides free access to all forms of contraception, which helps. But many pediatricians aren’t trained in inserting LARCs.

So we need more women’s health clinics, yet, instead, some are being closed as casualties of abortion wars. Moreover, states and schools should embrace comprehensive sex education, teaching contraception, the benefits of delaying sex and, also, the responsibility of boys.

A starting point for the United States should be to rebuild Title X spending on family planning. Surely we can afford to spend as much in this area as we did back in 1980.

So, of course, let’s ask teenagers to show responsibility toward sex. But let’s demand the same of our politicians.