NINETEEN years after a district court first allowed gay couples to marry in Hawaii, the Supreme Court could be poised to do so nationwide. If so, its ruling will be final, unlike the one in Hawaii, which was swiftly rejected by voters. Everything hinges on how the nine justices respond to the two-and-a-half-hours of oral argument they heard on April 28th.

Popular support for gay marriage has surged (see chart). Some 27% of Americans supported it in 1996; today, 55% do. Nearly 400,000 gay couples have tied the knot, estimates Gallup. Over two-thirds of Americans live in states where same-sex marriage is legal. Only 13 states still ban it, including Ohio, Michigan, Kentucky and Tennessee, which are parties to the four cases before the court collectively known as Obergefell v Hodges.

These cases involve gay couples who have suffered because the state where they live frowns on same-sex marriage. For example, Pam and Nicole Yorksmith (pictured) were married in San Francisco but live in Kentucky. One day their four-month-old son had breathing difficulties. Pam rushed him to a hospital just over the border in Ohio. But the hospital did not recognise that a child can have two mothers, and Nicole’s name was already in their records. So Pam was not allowed to give a parent’s permission for doctors to treat her child. It took an hour for hospital staff to reach Nicole, as the baby coughed and wheezed. All the other couples have tearjerking stories, too. Indeed, such stories are now common (see article), as is inevitable when some states allow marriage equality and others don’t.

The argument for striking down state bans on same-sex marriage is simple. The constitution says that no state may deny anyone within its jurisdiction “the equal protection of the laws”. Telling gay people they cannot marry would appear to violate that. Also, the constitution requires each state to give “full faith and credit” to “the public acts, records, and judicial proceedings of every other state”. This suggests that gay marriages performed legally in one state should be valid in others.

Arguing in favour of the state bans, John Bursch, a lawyer for Michigan, contended (seven times) that changing the definition of wedlock would bring undesirable consequences for society. Marriage would become unmoored from its raison d’être: raising children. A child who grows up “believing that marriage is about keeping that couple bound to that child forever” might fare better than a child whose parents’ marriage “is more about their emotional commitment to each other,” he said.