Right now, many same-sex couples are getting married in California. Recently, the California Supreme Court overturned the ban on same sex-marriages. Though few realize that two aspects of California’s same-sex marriages are unlike Massachusetts’, and they could redefine marriage in every state. And this issue is heading straight to the November election.

On May 14, by a 4-3 vote, the California Supreme Court voted on the right to same-sex marriage. Shortly thereafter, supporters of traditional marriage proposed a constitutional amendment on the ruling, defining marriage as an act between a man and a woman.

These supporters petitioned the California Supreme Court to stay their May decision pending the people’s vote in November. But the California court denied that petition about a week ago, making it certain that same-sex marriages in the state are now legal.

What’s happening now in California is different from what happened with same-sex marriage in Massachusetts in 2003, and those differences could remake marriage across America.

First, California has a civil-union law. Same-sex couples already can enter into civil unions that grant many legal benefits of marriage. The 4-3 vote was on whether giving every benefit of marriage is sufficient, or if the California Constitution demands that gays get more by calling it marriage. This lawsuit was not over equal benefits; homosexuals already had that in California. The lawsuit was over redefining marriage to include homosexuals.

Second, Massachusetts law requires a person must be a Massachusetts resident to be married there. California has no residency requirement. This means that starting today, homosexuals from all over the country can fly to California, get married, and fly directly back home.

Once there, they will file suit in federal court demanding that their home state recognize them as married. This will lead to a constitutional showdown in the U.S. Supreme Court, and it is a lawsuit some legal analysts say that supporters of traditional marriage may lose.

Congress passed, and Bill Clinton signed, the Defense of Marriage Act in 1996. The law specifies that if one state creates same-sex marriage, then other states do not need to recognize that marriage. Same-sex couples from other states getting married next week in California will be able to challenge DOMA’s constitutionality in court.

The Full Faith and Credit Clause of the U.S. Constitution requires every state to accept the legal enactments of other states even if it is illegal in one’s home state. This includes marriage. That’s why if you get married in Texas, then move to Ohio, the state of Ohio must accept you as a married couple even though you were not married in Ohio.

The Full Faith and Credit Clause also applies to residency requirements, blood tests, marriage counseling, waiting periods, and any other requirements. If you legally get married in any state, then all 50 states must accept it. Some say that the exact wording of the Full Faith and Credit Clause allows Congress to pass a law like DOMA. Others — including some conservatives — disagree.

With lawsuits being filed over the rest of this year in every state in the country, the outcome may well be that every state in America will have same-sex marriage, no matter what the people of each state want. If that happens, then the only way to restore traditional marriage would be passing the Federal Marriage Amendment.

Unfortunately for conservatives, it may take two or three years before the U.S. Supreme Court decides this issue. But if the American people make this an issue now, it could force the candidates to take a clear stand on marriage, giving voters something to consider in casting their vote. Americans should wake up to what is at stake with the next president’s nominations to the Supreme Court.

Mr. Blackwell is a contributing editor of The New York Sun.