A federal judge just declared DACA unlawful. Here’s what that means.

On Friday, a federal judge in Texas blocked an Obama-era program protecting undocumented immigrants who arrived in the US as children from deportation, halting the program’s ability to accept new applicants and once again throwing the lives of more than 600,000 people into tumult.

In his 77-page opinion, district court Judge Andrew Hanen concluded that the Deferred Action for Childhood Arrivals program, or DACA, is unlawful because it violates the Administrative Procedure Act, which governs federal rulemaking, by evading the normal “notice and comment” process in adopting new rules.

Hanen’s decision doesn’t immediately...