So a federal appeals court in New York has now become the second in the country to rule the Defense of Marriage Act unconstitutional. This is a key legal breakthrough, but it’s an even bigger deal if you step back and consider what the landscape might look like in a year or so. What’s happening is quite striking.

DOMA defines marriage as a union between a man and a woman, enshrining into law the federal government’s non-recognition of gay marriage. Today’s decision is important because it relies on a sweeping rationale for invalidating this, one that bodes very well for gay marriage proponents when they argue this case before the U.S. Supreme Court next year. As Ian Milhiser explains, Dennis Jacobs, the conservative judge who wrote the ruling

is not simply saying that DOMA imposes unique and unconstitutional burdens on gay couples, he is saying that any attempt by government to discriminate against gay people must have an “exceedingly persuasive” justification. This is the same very skeptical standard afforded to laws that discriminate against women. If Jacobs’ reasoning is adopted by the Supreme Court, it will be a sweeping victory for gay rights, likely causing state discrimination on the basis of sexual orientation to be virtually eliminated. And the fact that this decision came from such a conservative judge makes it all the more likely that DOMA will ultimately be struck down by the Supreme Court.

This bodes well long term for ending DOMA for good. Prominent gay rights advocate Richard Socarides explains to me what it will mean if that happens: “The government will give full federal recognition to same sex marriages in the states where that is now allowed. That means couples that are married, for instance, in New York will be entitled to all the federal benefits that any other married couples are entitled to.”

Now consider another aspect to all this. The decision comes on the same day as the Post released a new poll finding that a majority of likely voters in Maryland support a state referendum upholding a state law making gay marriage legal. If that passes, it will be the first time gay marriage has been ratified by popular vote. Voters in Maine and Washington State will also vote this fall on similar referendums, and polls suggest they may pass, too.

If they do pass, that will make gay marriage legal in nine states. And next year, if the Supreme Court rules DOMA unconstitutional — something that became more likely today — the government will have to accord full federal recognition to all the gay couples that marry in all those states.

“At some point next year, gay marriage may be legal and fully recognized in states covering more than 25 percent of the U.S. population,” Socarides says. “If that happens, there will be no turning back.”

The next step is to get the Supreme Court to rule that there is a federal constitutional right to same sex marriage for all gay Americans in every state. The Supreme Court may hear arguments over California’s Proposition 8 next year, so this could come up before the High Court. But even if the Prop 8 case doesn’t result in a constitutional right to gay marriage, today’s events are a reminder that it’s only a matter of time until it is legal in a wide swath of states — with gay married couples enjoying full recognition from the federal government. It’s not a matter of if, it's a matter of when.