The 1996 Defense of Marriage Act, which overwhelmingly passed Congress on a bipartisan basis, is the law that defines marriage for the federal government as the union of one man and one woman. It has now come under fire from legal challenges in the nation's court system.

A lesser-known part of DOMA is a provision known as Section 2. This section protects the rights of states to recognize as marriage only those relationships that are consistent with its laws. And many states have relied upon Section 2 in order to preserve marriage within their borders. As we have recently seen, successful efforts to redefine marriage in Maryland and Maine, for example, have not forced Texas and Florida to follow suit.

Most Americans seem to mistakenly assume that federal lawsuits aren't about their state's marriage laws. After all, those seeking to redefine marriage aren't attacking Section 2 of DOMA ... or are they?

Of more than 20 lawsuits filed by activists nationwide against DOMA, none has expressly targeted Section 2 or cited it as problematic. Take, for example, the DOMA case that is to be heard by the U.S. Supreme Court next month, United States v. Windsor. It challenges only the federal government's definition of marriage as one man and one woman for tax benefit purposes.

But Ms. Windsor's tax case out of New York couldn't force marriage to be redefined in Texas, Nebraska or even a U.S. territory like Puerto Rico, could it? After all, every state has the right to maintain marriage under Section 2, right? Well, not exactly.

By making a constitutional claim for a new federal definition of marriage, Windsor is asking the Constitution that binds all of us to impose her view of marriage upon everyone. If the U.S. Constitution is interpreted to require same-sex marriage, it doesn't require it in one place and not another. The U.S. Constitution will require it everywhere. So much for Section 2 of DOMA.

You wouldn't know this, however, by listening to some of those advocating for marriage to be redefined. Despite what they say, they are seeking a nationwide legal change -- yes, even in Arizona, Michigan, Georgia and any place else you can find good apple pie.

Consider the words of the best-known advocate for redefining marriage, President Obama: "What you're seeing is, I think, states working through this issue in fits and starts, all across the country. Different communities are arriving at different conclusions, at different times. And I think that's a healthy process and a healthy debate. And I continue to believe that this is an issue that is going be worked out at the local level, because historically, this has not been a federal issue, what's recognized as a marriage."

But what the president's statement conceals is that by supporting same-sex marriage and refusing to defend DOMA in court (something the Department of Justice has not done for two years now), our president is endorsing same-sex marriage as a constitutional matter. And if required by the Constitution, the redefinition of marriage won't be limited to Washington, D.C., or states that have expressly redefined it. Rather, it will apply nationwide, just like our right to vote, our right to remain silent and our right to freely speak our minds.

So when you hear people talk about the marriage cases going before the Supreme Court in March, don't be lulled into the belief that they have nothing to do with you. To the contrary, they affect every state and every American.

Austin R. Nimocks is senior counsel with Alliance Defending Freedom and a member of the legal team defending the California marriage amendment before the U.S. Supreme Court.