A mere 36 days have passed since President Barack Obama “solemnly” swore to “faithfully execute the office of president of the United States and will, to the best of my ability, preserve, protect and defend the Constitution of the United States.” It is surprising, then, that a move by the Department of Justice on Friday should make it appear that he has since forgotten what that oath entails.

Last week Obama’s administration stated that, in its opinion, the federal Defense of Marriage Act, which for purposes of federal tax benefits, medical protections and the benefits of entitlement programs recognizes only heterosexual married couples, is unconstitutional. Since the federal government is the defendant in a case that the Supreme Court will hear on this issue, such news is confusing and worrying.

With such a move, Obama has apparently seen fit to selectively support the rule of law.

That principle is as old as the Constitution itself. Alexander Hamilton wrote in Federalist No. 78 that “No legislative act, therefore, contrary to the Constitution, can be valid. To deny this, would be to affirm that the deputy is greater than his principal; that the servant is above his master; that the representatives of the people are superior to the people themselves; that men acting by virtue of powers, may do not only what their powers do not authorize, but what they forbid.”

The power to correct such imbalance between policy and the Constitution, Hamilton explained, “is the proper and peculiar province of the courts. A constitution is, in fact, and must be regarded by the judges, as a fundamental law. It therefore belongs to them to ascertain its meaning, as well as the meaning of any particular act proceeding from the legislative body.”

It is not, then, the president’s responsibility to argue that laws are unconstitutional and then refuse to uphold them in the face of legal challenges. By doing so, he infringes on the powers of one-third of the government of the United States and fails to do his job as the executive branch of the U.S. government.

Obama may think the federal government ought to recognize same-sex marriages. He might be right. That is not the issue. What is important in this development is that, contrary to his administration’s apparent belief, he does not have plenary powers over the laws of this country.

If the president wishes to truly be the unitary representative of the American people, as he argued he was after the elections (when he said, “our job now is to get a majority in Congress to reflect the will of the American people”), then he ought to defend all the laws of the United States, not just the laws of which he approves.

The Constitution states that all laws made in pursuance of it are “the supreme law of the Land.” Even if the case to not overturn the federal Defense of Marriage Act looks hopeless and the prospects look bleak, the president has an obligation to the American people who elected him to seek to keep that law, like any other law, in effect.

The law is the law, until repealed or ruled unconstitutional. Neither of those has yet happened.