How does that nursery rhyme go? First comes love, then comes marriage, then as many concurrent marriages as you want?

That may not be a completely far-fetched update of an old classic.

The percentage of Americans who find polygamy to be morally acceptable has more than doubled since 2001, according to new results of a Gallup survey tracking opinions on key moral issues since the early 2000s. In 2001, only 7 percent of Americans deemed polygamy morally acceptable. Now, 16 percent say they do not find it objectionable.

Is polygamy a serious contender for the next moral and constitutional marriage debate in the United States? Will the legalization of same-sex marriage actually open the door for plural marriage as some of its opponents have argued, or is there a limit to polygamy’s seemingly meteoric rise in acceptability?

Polygamy is still far from popular but support for the practice is gathering quiet momentum and its moment could arrive sooner than anticipated. Writing for The New York Times last weekend, conservative columnist Ross Douthat predicted that polygamy could be legalized in the United States as soon as 2040, given the rate of change in its acceptance.

Brad Wilcox, director of the National Marriage Project (NMP) at the University of Virginia, more or less agrees with that prediction. In a phone interview, he told The Daily Beast that there is no way to predict when or if polygamy will become law but, if it does, it could happen within “the next 20 to 30 years.”

Although that may seem sudden, polygamists have managed to find moral support with surprising speed. Of all the issues tracked by Gallup—including items as diverse as abortion, gambling, stem cell research, and wearing fur—the shift in Americans’ approval of polygamy over the past 15 years is most dramatic, matched only by a doubling of support for human cloning over the same period.

Same-sex relationships, divorce, and extramarital sex have all enjoyed considerable increases in public support since the early 2000s but polygamy has been something of a dark horse, finally crossing the threshold from being a fringe issue to becoming a practice that more than one in seven Americans could condone.

Even more surprising: Americans are now far more accepting of polygamous marriages than they are of extramarital affairs in monogamous marriages—proof, perhaps, that quality really does matter more than quantity.

But what’s behind this spike in polygamy’s popularity? It’s easy to point to television shows like Sister Wives and Big Love—as Douthat does in his Times op-ed—as evidence that polygamy has received the voyeuristic blessing of American pop culture. And it’s even easier, as a self-professed “slippery sloper” like Douthat also proves, to position polygamy as the logical endpoint of LGBT acceptance.

In his column, Douthat writes, “Can a cultural left that believes in proliferating gender identities and [Caitlyn] Jenner’s essential womanhood draw the line, long-term … [at polygamy]?”

But the social forces behind polygamy’s rise from obscurity run deeper than HBO and they exceed the logic of LGBT advocacy. In the United States, polygamy exists at a curious intersection of social libertarianism, religious fundamentalism, and radical polyamory—strange bedfellows in every sense of the term.

For his part, Brad Wilcox of the NMP attributes polygamy’s increasing popularity to “an increasingly libertarian or laissez-faire view that many younger Americans take toward sex, marriage, and family life.” In other words, support for polygamy may not be the bottom of a slippery same-sex marriage slope but rather a shared outcome of changing beliefs about the government’s role in family building.

Some far-right commentators—like Daniel Greenfield at Frontpage Mag—are already heralding the Gallup survey as a sign of “collapsing values,” but polygamy seems to be as much a product of a distinctly conservative belief in limited government as it is the result of social liberalism run amok.

Yet even though support for polygamy might be increasing in several ideological corners of the United States, it will be difficult for its practitioners to curry the favor of the majority.

Rough estimates place the polygamous population in the U.S. somewhere between 50,000 and 100,000 people, chiefly in Muslim and fundamentalist Mormon families. Basic moral acceptance from 15 percent of Americans does not necessarily translate into political advocacy for an extremely small population that already exists on the religious margins of the U.S.

Studies have also shown that polygamy may be detrimental to women and children as well as lower-status men who are ostracized by its practice. The vast majority of polygamous families in the United States and worldwide are polygynous (men with more than one wife) rather than polyandrous (women with more than one husband).

In the context of these polygynous arrangements, polygamy has been linked to everything from domestic violence to heart disease to crime to mental health problems for young children—and all this in addition to high-profile cases of rape and child sexual abuse that have emerged from the Fundamentalist Latter-Day Saint (FLDS) community in recent years.

This leads experts like Wilcox to conclude that polygamy is “a step in the wrong direction,” as he wrote for The New York Times, one that conflicts with a commitment to “women’s rights [and] child well-being.”

On paper, then, it might be difficult to raise a constitutional objection to polygamy—Justice Scalia suggested as much during the April hearings for Obergefell v. Hodges—but in practice, polygamy is associated with a host of social problems that would weigh it down in any bid for legitimacy.

Two years ago in Brown v. Buhman, the Supreme Court may have ruled in favor of allowing multiple cohabitation but the legalization of plural marriage, if it ever comes, will be hard-fought.

But that won’t stop it from becoming a bizarre cause célèbre in the coming decades. Some feminists, like Jillian Keenan writing for Slate, have tried to make a case for polygamy under the guise of a woman’s right to choose her spouse(s). Keenan also supports polygamy as an option for the polyamorous, an emerging term favored by social liberals used to refer to people in relationships with multiple partners who may not necessarily be of the same gender.

Pro-polygamy op-eds also appear with surprisingly regularity on outlets as varied as CNN, Vice, and The Economist. These pieces become momentary flashpoints of online discussion but never gather steam beyond that. And, of course, Biblical conservatives, libertarians, and fundamentalists continue to make their own cause for polygamy as an Old Testament practice, a civil liberty, and a matter of religious freedom, respectively.

Whereas same-sex marriage supporters managed to build a broad coalition around a relatively small percentage of the U.S. population, proponents of polygamy face a scattered field of sexual radicals, conservatives, and columnists looking for a counterintuitive argument.

But stranger coalitions have found success in the past. Given the Gallup data, too, it’s possible that polygamy could be legalized if acceptance continues to increase at its current pace in spite of social concerns. For now, however, polygamy faces obstacles more numerous than the Sister Wives’ children.