What lessons will same-sex marriage advocates take from New York into future legislative battles? Here are three to consider:

To pass a bill, you need a governor, probably a Democrat, who is willing to do more than just say he’ll sign it. An article in Monday’s Times detailed New York Governor Andrew Cuomo’s one-on-one campaign aimed at undecided legislators: “ ‘I can help you,’ Mr. Cuomo reassured them in dozens of telephone calls and meetings, at times pledging to deploy his record-high popularity across the state to protect them in their districts. ‘I am more of an asset than the vote will be a liability.’ ”

“New York was significant,” says Patrick Egan, a political scientist at New York University who studies public opinion on gay rights, “because we saw a popular Democratic governor put his reputation and a lot of political capital on the line.” And since that governor is a smart and consummately political guy, we can figure that he did so not only because he thought he was doing the right thing, but because he believed this issue was a winner. “That’s the first time we’ve seen that in this particular civil rights movement,” Egan says.

After New York, the next state to approve same-sex marriage will likely be Maryland. In February, it came very close to doing so. The state senate voted in favor of a marriage-equality bill that lost momentum and did not come up for a vote in the House of Delegates. Maryland’s state legislature had a couple of factors to contend with that New York’s did not: in particular, an organized opposition led by black churches. But mainly what it lacked was a governor as willing to identify himself with the issue as Cuomo was. Same-sex-marriage advocates in Maryland say they will push Governor Martin O’Malley to do more in next year’s legislative session, when they plan to reintroduce a marriage bill. “We know he’s an ally, and would sign a bill,” says Patrick Wojahn of Equality Maryland, “but we want him to go a step further.”

Perhaps they should borrow a line of persuasion from the activist Chad Griffin, who heads the foundation supporting the lawsuit against California’s Proposition 8. “Cuomo,” Griffin says, “is going to be seen as a civil rights hero of this generation, and he will reap tremendous benefits from that. He’s going to have a giant donor base in any Presidential run. All he has to do is start pushing a button.”

Moderate Republicans can be convinced—especially if they happen to have a gay relative, and/or a libertarian streak. The Times story chronicles how Cuomo lined up Republican moneymen, one of whom, the billionaire Paul Singer, has a gay son. In the legislature, a few moderate Republicans of more libertarian leanings regretted having voted against a gay-marriage bill in 2009. Cuomo targeted them, and it worked. In the end, the 33-29 vote in the Senate included four Republican ayes.

“This starts to look a little like the civil-rights movement in the sixties,” Egan says, “where you see one party pushing for an expansion of rights, and enough cracks opening in the other party that you start to get bipartisan consensus.”

Of course, a lot depends on what happens to the senators, the Republicans in particular, who voted for the gay-marriage bill. The leading anti-gay-marriage group, the National Organization for Marriage, has pledged to raise two million dollars to defeat them in the next election. Fence-sitters in other states will be watching.

The practical stuff can create its own momentum. As more same-sex couples marry, and, inevitably, move to other states, break up, undergo the death of one spouse, and all the other things that straight married couples do, questions are going to come up that will need resolving. They already have. Advocates for same-sex marriage would do well to point out the crazy quilt of legal confusion, along with the classes of unequal citizens this creates.

In Maryland, for example, attorney general Douglas F. Gansler said in February that his state should recognize valid same-sex marriages from other states. That’s not legally binding on the courts, though, and that has made for some contradictory rulings from Maryland judges—a tendency that is clearest so far in the realm of divorce. As an item on the Baltimore Sun Web site this week points out, same-sex couples who married in states where these unions are legal and have since sought divorces where they now live, in Maryland, have met with a bewildering set of responses. In the cases brought so far, the Sun reports, one judge approved the divorce petition brought by two women, but other judges have not—and in one case, did, then reversed the decision.

And divorce is not the only context in which the validity of same-sex marriages performed elsewhere has become a point of contention. In a recent domestic-abuse case in Maryland, a woman who had married another woman in Washington, D.C., where same-sex marriage is legal, invoked spousal privilege to avoid testifying against her wife in a domestic-abuse case. The judge permitted her to, and her spouse was acquitted of threatening her with a knife.

The issues are manifold, and a bit dizzying. “If two guys are married in New York,” Egan asks, “can one of them move to Indiana and marry a woman?” Would it be bigamy? Pile up enough questions like this, and you sort of force the issue.

Which is one reason that, for many advocates of same-sex marriage, the real lesson is that a federal solution would be the best outcome of all. Griffin, whose own efforts are directed toward seeing bans on gay marriage declared unconstitutional by the Supreme Court, was especially frustrated with President Obama’s comments last week. Obama reacted to the news from Albany by reëmphasizing that same-sex marriage was a matter best left up to the individual states. “We were O.K. with ‘evolving,’ but this is going backward,” Griffin says. “I come from Arkansas. What do I tell a gay teen-ager there? That you’ve got to move to Massachusetts or New York so you can be equal? At the end of the day this is a federal issue.”

Photograph by Bryan Smith/ZUMA Press/Corbis.