One way or another, the issue of gay marriage seems squarely headed to the Supreme Court.

Two federal appellate court decisions, one in Massachusetts and the other in California, have set the stage for challenges to federal and state laws limiting marriage to a union between a man and a woman. But the bigger news is that a confrontation in the court, which many civil libertarians and gay rights activists originally feared would come too soon, now seems to be proceeding at just the right pace.

The politics of gay marriage have changed, and that cannot help but affect the legal battle. Courts can only get so far ahead of the public, and in this case, they aren't nearly as far ahead as they would have been a few years ago.

In the Massachusetts case, which challenged the federal Defense of Marriage Act's prohibition of benefits to married same-sex couples, the United States Court of Appeals for the First Circuit held that the federal law unconstitutionally interfered with the autonomy of states, in this case Massachusetts, to define marriage.

Now, for anyone who followed the recent arguments on Obamacare, you may remember that it was conservatives who were pushing the argument that the federal government couldn't tell states what to do about health care. In the gay marriage case, by contrast, the state is using the same argument to support the liberal position that the federal government can't tell them which marriages can be recognized.

In theory, federalism has always been a double-edged sword, usually wielded based on political considerations. But in recent years, at least, it has been the conservative justices who have used federalism to strike down federal laws limiting state autonomy. Certainly that was the thrust of the argument you heard on Obamacare from the four-man bloc led by Justice Scalia. So what do conservatives do now that the table has turned? Stand by their usual dedication to state autonomy, or rule that it doesn't matter when it's same-sex marriage at issue?

In the California case, the state Supreme Court originally held that same-sex couples were entitled to marry under the California Constitution. The Prop 8 initiative, passed by the voters, overruled that decision. With real concern and indeed some opposition from the gay community afraid of teeing up the issue for defeat, a coalition brought suit in federal court claiming that Prop 8, in revoking the right to marry, was itself unconstitutional.

The district court so held; the Ninth Circuit panel, by a vote of 2 to 1, upheld that decision, and the court as a whole, over four dissents, ruled on Tuesday that it would not rehear the case before a panel of 11 judges, known as en banc review.

That means the next step, which the losing side has vowed to take, is to appeal to the Supreme Court.

Now, the Supreme Court can always decide not to hear cases, even those that technically are appeals as of right. Neither case raises the unadorned question of whether the Constitution requires that states grant marriage licenses to same-sex couples: The Massachusetts case is about the autonomy of a state that chose to do so; the California case raises the issue of whether a state, having granted the right, violates the Constitution when it takes it away.

Even so, reversal in either would be a major blow for the proponents of same-sex marriage; affirmance, a major triumph. The betting is that one or both of these cases will end up in the Supreme Court -- and with a decent, maybe very decent, chance of winning.

How things have changed. The gay marriage issue today is in a different place from where it was a few short years ago. The sky didn't fall in Massachusetts. It isn't falling in New York -- or Connecticut or New Hampshire or Vermont. The president himself has endorsed it, which is something no national candidate would do even in 2008. And while the polls can be read both ways, no one thinks Obama stands to lose ground by his support.

Perhaps more to the point, it seems clear which way the wind is blowing. Sooner or later, and probably sooner than anyone would have dared predict, same-sex marriage will be accepted for what it is: a matter of personal choice that is really no one's business beyond the two people involved.

Susan Estrich is a columnist, commentator and law and political science professor at USC.