WASHINGTON — Three US states and three countries have approved same-sex unions just in the two months since the Supreme Court heard arguments on gay marriage, raising questions about how the developments might affect the justices’ consideration of the issue.
In particular, close observers on both sides of the gay marriage divide are wondering whether Justice Anthony Kennedy’s view could be decisive since he often has been the swing vote on the high court.
“It is always possible that Justice Kennedy is reading the newspapers and is impressed with the progress,’’ said Michael Klarman, a Harvard University law professor and author of a recent book on the gay marriage fight.
In earlier cases on gay rights and the death penalty, Kennedy has cited the importance of changing practices, both nationally and around the world.
The court is expected to rule by late June in two cases involving same-sex marriage.
One is a challenge to California’s voter-approved Proposition 8 that defines marriage as the union of a man and a woman. The other seeks to strike down a portion of the federal Defense of Marriage Act that denies to legally married same-sex couples a range of benefits generally available to married heterosexuals.
The justices took an initial vote in the days after hearing arguments in the two cases in late March. The senior justice on the winning side and the senior justice in dissent assigned opinions based on those votes. But while that first vote is important, it is not the end of the process; justices’ assessments of a case can shift subtly or, in some cases, dramatically.
In 1992, Kennedy initially drew the assignment to write a majority opinion for five justices allowing prayers at public school graduations. In the end, he ended up writing the opinion for a different five-justice majority striking down the graduation prayers. According to several accounts, Kennedy simply changed his mind during the writing process.
Current events also can find their way into opinions. Last year, Justice Antonin Scalia’s fiery dissent from a court ruling that watered down Arizona’s crackdown on immigration included a reference to comments President Obama made at a news conference that took place between the argument in the case in April and the announcement of the decision in June.
There is no way to know at this point whether anything similar will occur in the gay marriage cases, either of which could be decided on technical legal grounds that would say little about the court’s view of the issue. But there has been no shortage of action.
In a 10-day span this month, Delaware, Minnesota, and Rhode Island gave final approval to bills to legalize same-sex marriages. Minnesota became the 12th state, as well as the District of Columbia, to approve same-sex unions. The other nine are: Connecticut, Iowa, Maine, Maryland, Massachusetts, New Hampshire, New York, Vermont, and Washington.
And more change could come soon. The Illinois Senate has approved a gay marriage bill that now is pending in the state House in advance of the May 31 end of the legislative session. Governor Pat Quinn has said he would sign it.
Both sides in the high court gay marriage debate say the recent events reinforce arguments they made to the court in March.
Defenders of limiting marriage to heterosexuals say the justices need only look at the change in marriage laws to see that there is no reason for them to declare a national rule for gay marriage that would upend constitutional bans in 30 states and laws prohibiting same-sex unions in roughly half a dozen others.
‘‘These developments provide yet further evidence . . . that the claim that gays and lesbians are politically powerless and that the courts therefore have some special role in subjecting classifications affecting them to strict scrutiny is baseless,’’ said Ed Whelan, an opponent of same-sex marriage and president of the Ethics and Public Policy Center.
Jim Campbell, a lawyer for Alliance Defending Freedom, said the court should not short-circuit a national debate.
‘‘The vast majority of the states have decided to retain the traditional view of marriage that has existed throughout Western civilization. This decision belongs to the people and should be decided by the people,’’ Campbell said.
Mary Bonauto, the director of the Civil Rights Project at Gay and Lesbian Advocates and Defenders, said the assessment of the political clout of gays and lesbians is misleading. The number of states allowing same-sex weddings has doubled in less than a year and now represents 18 percent of the US population. If Illinois joins in and the court were to affirm a lower court decision that struck down the California ban, just over a third of the population would live in 14 states and the District of Columbia where gay marriage would be legal.
That is not nearly enough, especially in the context of a decades-long struggle by gays and lesbians to win the right to marry, Bonauto said. ‘‘These states moving in the direction of marriage is a far cry from all states doing it,’’ she said.