The Supreme Court handed down major victories for gay marriage. The Post’s Robert Barnes breaks down the DOMA and Proposition 8 decisions from the courthouse steps. (The Fold/The Washington Post)

The Supreme Court moves incrementally. And, very often, inexorably.

Seedlings planted take root. And that is why the careful, limited and even technical rulings announced Wednesday, the first time the court has squarely confronted the issue of same-sex marriage, hold such importance for the future.

Ask an expert — Justice Antonin Scalia.

He all but sounded a fire alarm when Justice Anthony M. Kennedy said the court’s majority opinion in U.S. v. Windsor, which struck down a crucial part of the Defense of Marriage Act, was built on a bedrock of respect for a state’s ability to define marriage and “confined to those lawful marriages” that states decided to sanction.

Scalia warned that the opinion by Kennedy and the court’s liberals was not actually a toast to federalism; it was larded with language that provided a road map for challenging the states that do not allow same-sex marriage.

“By formally declaring anyone opposed to same-sex marriage an enemy of human decency, the majority arms well every challenger to a state law restricting marriage to its traditional definition,” Scalia wrote.

Challenges to states that don’t allow gay marriage are inevitable.

“No one should be fooled; it is just a matter of listening and waiting for the other shoe,” Scalia said.

History provided such a lesson, and it involved those same justices.

It was exactly 10 years ago Wednesday that Scalia unloaded a similar broadside against Kennedy’s majority opinion in Lawrence v. Texas, which held that states “demean” gays by “making their private sexual conduct a crime.”

That decision, too, was cast as a narrow one, but Scalia was not buying it.

If the court’s reasoning is right, Scalia asked, “what justification could there possibly be for denying the benefits of marriage to homosexual couples . . . ?”

Justice Ruth Bader Ginsburg, who joined both of those Kennedy opinions, talked about what the court’s role should be in moments of great social change during a recent question-and-answer session at the University of Chicago Law School.

She repeated her criticism that Roe v. Wade moved too far, too fast.

“Judicial restraint” is a better alternative, Ginsburg said. “The court can put its stamp of approval on the side of change and let that change develop in the political process.”

Or the judicial one. That was on display a day earlier at the court, when the court’s conservatives declared a key part of the Voting Rights Act unconstitutional.

Four years earlier, Chief Justice John G. Roberts Jr. held off on such a drastic step when the court considered a similar challenge.

The court found a narrow way out, and relieved liberal justices joined Roberts in a nearly unanimous warning to Congress that the law would be upheld for now but that there were serious questions about its constitutionality.

Congress took no action, and Roberts lowered the hammer Tuesday.

He reminded that “eight members of the court subscribed” to the view that there were serious constitutional problems and said Congress’s failure to correct them left the court “no choice” but to strike down the law.

That might have been on the minds of Roberts and Justice Samuel A. Alito Jr. on Wednesday. They wrote separate dissents in the DOMA case to draw attention to Kennedy’s line about the limited nature of his ruling rather than the broad language about “the evolving understanding of the meaning of equality.”

Wrote Alito: “To the extent that the court takes the position that the question of same-sex marriage should be resolved primarily at the state level, I wholeheartedly agree.”

Roberts emphasized that the majority’s judgment is “based on federalism” and “that power will come into play on the other side of the board” — an unmistakable reference to the constitutional right of states to ban same-sex marriage.

The trajectory of the court’s jurisprudence is never assured, of course. Alito’s replacement of Justice Sandra Day O’Connor changed the court’s course on issues such as abortion and campaign finance legislation.

No one knows what the court will look like when the follow-up case on same-sex marriage arrives at the court. But this is known: Ginsburg is 80, and Scalia is 77; Kennedy is soon to be 77, and liberal Justice Stephen G. Breyer turns 75 this summer.

Whichever president appoints their successors will have much to say about what comes next.