ON TUESDAY, Americans in Maryland, Maine and Washington state voted by almost identical four-point margins to extend marriage rights to gay and lesbian couples; in a fourth state, Minnesota, voters rejected a constitutional ban on same-sex marriage, again by about the same margin. With those ballot victories for marriage equality, the first after a 14-year string of defeats in 32 states, it is now reasonable to imagine a day in the not-very-distant future when marriage for gay and lesbian couples across this country will be unexceptional, unencumbered and mostly unremarked upon.

Maryland, Maine and Washington will become the seventh, eighth and ninth states, in addition to the District of Columbia, to permit same-sex marriage. (California did also, but only briefly, in 2008.) In Maine’s case, Tuesday’s vote neatly reversed the outcome of a similar referendum just three years ago that annulled a marriage law passed by the state legislature. Other states, including ones that have voted against marriage equality, are likely to follow suit. The tide has turned.

That judgment is not political crystal-ball gazing; it’s simple demographics. Acculturated by gay celebrities such as Ellen DeGeneres and Anderson Cooper, as well as by such popular shows as “Modern Family,” younger Americans regard gay men and lesbians as mainstream minorities and see no logic in discriminating against them. By large majorities, they are voting in favor of marriage equality.

By January, when the three new state laws will have taken effect, about 15 percent of Americans will live in states where it is legal for same-sex couples to marry. That is remarkable; the number was zero just eight years ago. It is especially heartening that the voters themselves, rather than courts and judges, are leading the charge in this latest crusade to expand the country’s stance on civil rights.

Still, 30 states have adopted constitutional amendments banning gay marriage, and others have laws on the books to the same effect. Even if the direction is clear, the path toward a universal right to marriage equality remains long.

One major unknown is the Supreme Court, which may soon weigh in on the Defense of Marriage Act, which denies federal recognition of same-sex marriages. Federal courts have ruled that the act deprives gay men and lesbians of the Constitution’s guarantee of equal protection. But they have also sidestepped the equally pressing issue of state measures to deny marriage equality. If the Supreme Court does enter the fray over gay marriage, it would do well to consider the results of Tuesday’s ballot questions and, more broadly, the clear trajectory of the nation’s shifting ­attitudes.