The Massachusetts Supreme Court ruled in Goodridge v. Department of Public Health in 2003 that state constitution required that same-sex couples be allowed to marry. State courts in California, Connecticut, and Iowa have since followed suit. As David Cole wrote recently in The New York Review of Books, the legal case for same-sex marriage is extremely strong. Equal protection clauses both in the federal Constitution and in our state constitutions make it difficult to deny the legal status of marriage to anyone on the basis of their gender or sexual orientation. The arguments against same-sex marriage—that it runs counter traditional ideas of what marriage is or is somehow intrinsically immoral—sound uncomfortably like the arguments that were used fifty years ago against mixed-race marriage.

Nevertheless many people are still uncomfortable with the idea of same-sex marriage, and the legal victories have triggered a broad political backlash. In 2004, after Massachusetts decision people in eleven states voted to amend their constitutions to outlaw same-sex marriage, with more following in 2006. Twenty-six states so far have passed constitutional amendments banning same-sex marriages, and most of the others have passed statutes against it. So it is not surprising that both Barack Obama and Hillary Clinton opposed same-sex marriage in the primaries. And while Obama campaigned on a promise to overturn the Defense of Marriage Act, which defines marriage exclusively as between a man and a woman, as President he has continued to defend the status quo.

Polls shows that supporters of same-sex marriage are still a minority. But that’s going to change. Because as Jeffrey Lax and Justin Phillips show, the strongest opposition to same-sex marriage comes from people over 65. People under 30 are about 35 percentage points more likely to say they support it. As Lax writes,

If policy were set by state-by-state majorities of those 65 or older, none would allow same-sex marriage. If policy were set by those under 30, only 12 states would not allow-same-sex marriage.

As more young people reach voting age and the older generation dies off, popular support for same-sex marriage will grow. Already an April ABC News/Washington Post poll found for the first time more people who supported same-sex marriage than opposed it. It may not be much comfort to those who are being denied the right to marry today, but it won’t be that long before advocates of same-sex marriage are winning elections as well as court victories.