The statute creates two classes of “removable” aliens: first, ordinary detainees who haven’t committed crimes but are facing removal on other grounds and, second, “criminal aliens” facing removal because of criminal convictions.

Once ordinary aliens are detained for removal, they face three different legal tests. First will be a “bond hearing,” at which they can try to convince an immigration judge that they can be safely released, and will show up for their deportation hearing. They can provide evidence of their community, and family members can attend to give their support. If they get bond, they can go back to their lives until their next hearing. Next, whether or not they get bond, they receive a “removal hearing,” at which they can try to show that they are not “removable” after all. If they win there, they are free to go. But even if they fail in that effort, they can still try to show that they are eligible for what is called “cancellation of removal”—for example, because they have been lawfully present in the U.S. for years and have family ties here, or because deportation would subject them to danger in their country of origin. If the immigrant can prove that claim, immigration authorities have the discretion to allow him or her to remain and “adjust” to legal status.

But go back to the beginning—the bond hearing. Some “criminal aliens” have been convicted of certain specified statutory crimes (such as drug or firearms offenses, sex offenses, terrorism or espionage, or crimes of “moral turpitude”). For this “criminal alien” group, the statute says that “when the alien is released” from imprisonment, the government “shall take [him or her] into custody.” These immigrants get no bond hearing; they must be held in detention until their cases are resolved. They can still challenge removal, and they can still ask for cancellation, but they must remain behind bars for the months or even years those proceedings can take.

This is the issue in Nielsen v. Preap: It is not whether authorities can detain these aliens; they can. But does the statute really deny bond hearings to all of them—longtime residents of the U.S. who were convicted of minor offenses five, 10, 15, or more years ago? What if a person has long ago been released and has returned to a community, established a family and put down roots, and lived a blameless life since that brush with the law? In other words, what if the immigrant would otherwise be a prime candidate for bond?

These aliens can be detained and deported. There is no question that ICE agents can show up at their homes, arrest them, and hold them for removal proceedings. But does the when language mean they don’t get a bond hearing? If a noncitizen has left prison and established a new life, did Congress, in writing the statute, really mean to deny that person the chance to show an immigration court that he or she will show up for a removal hearing, the way other “noncriminal” aliens can?