Same-sex couples began marrying Monday morning in some Alabama counties, despite an 11th-hour attempt by the state's well-known chief justice to prevent the marriages from going forward.

In a letter issued late Sunday night on the eve of same-sex marriage starting in the state, state Supreme Court Chief Justice Roy Moore told probate judges to follow state law rather than a ruling from a federal judge that legalized it. But the U.S. Supreme Court has now denied Alabama's stay request, making Moore's already-futile effort appear even moreso.

Here's why: Although the Supreme Court has denied stays in marriage cases before, the Alabama decision is the first since it announced it would decide whether the U.S. Constitution allows same-sex couples to marry regardless of individual state laws.

Many expect the court to rule in favor of nationwide gay marriage, and they see the lack of a stay in this case as confirmation of that. If the court weren't going to legalize gay marriage, they reason, it would be more likely to put Alabama on hold in the meantime.

"By refusing to halt marriage licenses in Alabama, the Supreme Court has telegraphed that there is virtually zero risk that they will issue an anti-equality ruling this summer," said Human Rights Campaign legal director Sarah Warbelow in a statement. "Instead, the odds of a ruling bringing marriage equality to all 50 states have increased significantly."

For years, the Supreme Court has stayed out of state marriage cases. That changed last year as states appealed a wave of lower-court decisions. In 2014, the Supreme Court denied stays in states including Alaska, Florida, Idaho and South Carolina. And in October, it decided not to hear appeals directly led to legalized marriage in Indiana, Oklahoma, Utah, Virginia and Wisconsin.

There are now 13 states where same-sex couples still cannot marry, a number that will continue to drop, barring the unforeseen. The Supreme Court's Alabama stay denial didn't explicitly answer the question of whether states have a right to define marriage as between a man and a woman, but following its decision to finally hear appeals this year, it symbolizes an escalation that it could strike down marriage bans nationwide.

Still, some Alabama counties, like Shelby County, said they would not issue any marriage licenses Monday, citing the conflict between state and federal instructions. Similar moves have been taken by counties in other states like Utah and Kansas following court rulings, and 14 states are currently considering bills that would exempt individuals from performing marriages for same-sex couples if they have religious objections to it.

But with every state marriage ban that falls and every same-sex couple that marries in places like Alabama and Oklahoma, these and other measures to stop same-sex marriage from eventually becoming legal nationwide seem more and more hopeless.

And Alabama might be the best example of this yet.