Editor's note: Mary Ziegler (@maryrziegler) is the Martin Luther King Professor of Law at UC Davis. She is the author of "Dollars for Life: The Antiabortion Movement and the Fall of the Republican Establishment" and "Roe: The History of a National Obsession." The views expressed in this commentary are her own. Read more opinion on CNN.

(CNN) — This week, Idaho passed the first law restricting travel for abortion. Framed as an "abortion trafficking" bill, it criminalizes anyone who helps a minor get an abortion or abortion pills without parental consent. Violators will face felony charges and up to five years in prison.

The law could treat anyone, from friends to grandparents, as traffickers. Even when parents consent, a defendant has to prove it using an affirmative defense, a job that usually belongs to prosecutors. Idaho Republicans presented the bill as a common-sense protection of parental rights. State Representative Barbara Ehardt, one of its sponsors, described it as a tool to "go after those who would subvert a parent's right to be able to make those decisions in conjunction with their child."

But make no mistake: Idaho's bill is part of a broader attack on the right to travel for adults as well as minors, and the stakes of whittling away at that right are higher than ever.

To understand the intent behind the law, we can simply look at where it came from. It draws directly from a model developed by the National Right to Life Committee, a major national antiabortion group, in the summer of 2022. The model stressed that it would not be enough to enforce abortion bans, given that people could take advantage of "existing State laws on telehealth and the proximity of States with less protective laws" to circumvent criminal abortion laws. Idaho's abortion trafficking law was presented not just as a step to protect parents, but part of a broader way to curtail abortion-related travel.

Starting with minors is a natural way for abortion opponents to test the waters of a legal prospect that — as a state law that openly seeks to restrict the ability to travel from one state to another by choice — seems to challenge a fundamental tenet of both federalism and freedom.

The law directly echoes a federal law on the sex trafficking of minors, which criminalizes those who "knowingly recruit, entice, harbor, transport, provide, obtain, or maintain a minor" for the purpose of commercial sex acts, regardless of whether the minor was forced, coerced or deceived into that act. When Idaho's law is challenged, as it surely will be, abortion opponents will likely tell courts that if one law is legal, the other must be too.

And they will stress that courts sometimes carve out narrower rights for minors. We often take for granted that minors do not have the right to vote, even if the Constitution protects access to the ballot for adults. In the context of abortion, when the Supreme Court still recognized abortion as a fundamental right, judges upheld laws requiring minors to notify their parents or get their consent before terminating a pregnancy.

Never mind that a similar law would not stand if it applied to adults — the Court at the time struck down a law requiring married women to get their husbands' permission. If Idaho wants to go after the right to travel, focusing on minors seems to be a logical place to start.

But if attacks on the right to travel accelerate, there will be a far more wide-ranging fallout. The right to travel is venerable: since 1823, the Supreme Court has recognized the "right of a citizen of one state to pass through, or to reside in any other state."

The Supreme Court also addressed the idea of a right to travel in cases from the 1940s and 1960s. In Shapiro v. Thompson in 1969, it struck down laws setting minimum length-of-residency requirements for those seeking welfare. The Court stressed that "our constitutional concepts of personal liberty ... require that all citizens be free to travel throughout the length and breadth of our land uninhibited." The Court reaffirmed this idea in 1999 in Saenz v. Roe, which struck down a similar durational residency requirement, stressing that the right was so vital that it could be enforced when either private citizens or the government violated it.

But in recent years, as the nation becomes more polarized, the stakes of free travel seem higher. In 2008, author Bill Bishop identified what he called the Big Sort: Americans, he argued, were moving partly to live near those who agreed with them politically. This sorting amplified the nation's political polarization; by 2004, half of Americans lived in counties where presidential elections were landslides. Since then, the number of super landslide counties — where a president won 80 percent or more of the vote — almost quadrupled.

If identity-related moves are deepening polarization, it is also increasingly important for Americans seeking to match their hopes for the future with the policies in their states. State legislatures — and often, state policy — have grown far more polarized in recent decades. The culture wars, together with the Covid-19 pandemic, have prompted the migration of Americans to states where they feel a sense of belonging. In the past several years, conservatives tired of mask and vaccine mandates moved from big progressive states to Texas or Florida.

Now, states with harsh abortion bans are seeing the exit of physicians and medical students who do not wish to navigate a new criminal regime. Parents of transgender children are sometimes fleeing states that restrict access to gender-affirming care.

For many Americans, the right to travel can be a kind of deliverance. The ability to move around allows people to avoid sanctions and even criminal charges for choices that are central to their identities. The right to travel lets people seek out like-minded communities and define how they see themselves.

If Idaho's experiment is a success, other threats to the right to travel will be coming. For now, Idaho is targeting people within the state who are directing minors on how to obtain pills or procedures out of state, but other proposals floated by the antiabortion movement are more expansive, such as bills, modeled on Texas's SB8, that could allow bounty hunters to sue anyone who has an abortion out of state — even if those actors were following the law in the state where the abortion took place.

If one state can so easily regulate what happens outside its borders, it will gut the freedom for Americans to seek sanctuary in places that suit them politically. It will not be a healthy sign for our democracy.

In theory, voters can opt for the politicians and policies they prefer. But if courts begin gutting the right to travel, states could make it much harder for their citizens to cross borders. They may even try to apply their own criminal laws and civil penalties to out-of-state actors who help people who have crossed state lines.

When the Supreme Court reversed Roe v. Wade, Justice Alito suggested that it was better to leave abortion politics to the democratic process. That way, the court implied, voters in each state could decide to go their own way, and if an issue mattered enough to someone, they could move to a place that reflected their views. But that is not what key abortion opponents in Idaho and other states like it are aiming for. They want to stop citizens from having abortions, anywhere, and for almost any reason. If the right to travel is a casualty of that fight, so be it.

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