Secretary of State John Kerry’s signature of the U.N. Arms Trade Treaty Wednesday was a serious error, one that will have far-reaching consequences for American foreign policy and American sovereignty. Those consequences will be even worse because the Senate, which has signaled many times that it is opposed to the treaty, will likely have no real opportunity to reject it.

It’s commonly said that the Senate has to provide its advice and consent to any treaty – commonly known as ratifying it – before it can take effect. That’s true, but there’s a loophole. Once the U.S. signs a treaty, we hold ourselves bound not to violate the treaty’s “object and purpose.”

In other words, we obey in practice treaties that the Senate has never ratified.

This rule is an old one, and it used to make some sense. It would be dishonorable to sign a treaty with another country, do all the things prohibited by the treaty, and then ratify it. But that was a different era.

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Today, treaties are not just about international conduct. They seek to regulate how we raise our children, how we treat the disabled, and how we manage our firearms market.

As a result, the old requirement not to violate the “object and purpose” of a signed treaty has become a way to evade the need for Senate ratification. And in the case of the Arms Trade Treaty, the problem is even worse. The administration will argue that it already has all the powers it needs to enforce the treaty.

In the Gun Control Act of 1968 and the Arms Export Control Act, Congress gave the Executive Branch the power to control both the import and export of firearms – indeed, of weapons of all kinds. This power is virtually unfettered. All the president has to do is to assert that a particular firearm is not suitable for “sporting” purposes and, under the 1968 Act, he can ban its import.

We have recently seen an example of this with the executive actions banning the import of Korean War vintage M1 Garand rifles, which the White House justified as a gun control measure. And since many U.S. gun manufacturers rely on imported parts and components, or financing and insurance from abroad, the Treaty also gives other countries new opportunities to affect the U.S. firearms market.

But it is the Treaty’s vague norms that pose the biggest long-term problem. At the heart of the Treaty are terms like “international humanitarian law” and “international human rights law.” By committing itself to uphold these terms, the U.S. is binding itself to meet requirements that it does not define. That will affect not only our domestic firearms market but our foreign policy.

Over the coming years, the treaty’s proponents will seek to expand what those vague terms include. Since the U.N. has already defined gun control as a human right, they will not have to work very hard to make it part of the treaty. By signing the Treaty, the U.S. has tied itself to a conveyor belt: it is no longer in control of where it is going.

Opponents of the treaty are not powerless. Sen. Jerry Moran (R-Kan.), Sen. Jim Inhofe (R-Okla.), and other colleagues, along with Rep. Mike Kelly (R-Penn.) in the House, have made it clear that Congress is deeply skeptical about the treaty.

They can continue to voice their opposition, including by calling for hearings. In the end, a U.S. president can ‘unsign’ the treaty.

All of those actions are wise responses to a serious error by the Obama administration, one that will be a menace for years to come.