Zeroing in on North Texas, the attorney general’s office encouraged the Harrold Independent School District to adopt an anti-transgender bathroom policy. The choice of district was no accident. Though there was no controversy surrounding transgender students in Harrold, the state’s lawyers knew that any case challenging the federal policy brought there would be assigned to Judge Reed O’Connor of the Federal District Court for the Northern District of Texas.

They may have been confident that Judge O’Connor, who was appointed by President George W. Bush, would be sympathetic to their effort. In 2015, shortly before the Supreme Court legalized same-sex marriage, he blocked the implementation of a Department of Labor regulation allowing married same-sex couples to take family medical leave even if they lived in a state that didn’t permit same-sex marriage at the time.

Judge O’Connor on Sunday issued a preliminary injunction that prohibits the Education Department from enforcing its guidelines nationwide. In a 38-page order, he barred the federal government from taking enforcement action against discriminatory policies or practices.

The ruling, which the Justice Department is expected to appeal, may lead educators around the country to question whether they need to follow the Education Department’s transgender guidelines as the new school year starts. They would be wrong not to; the rules provide a common-sense approach that makes harassment and stigmatization of transgender students less likely.

Meanwhile, Mr. Paxton is determined to block another important protection for transgender people. On Tuesday, his office filed a new lawsuit against the Department of Health and Human Services over a regulatory change that sought to expand access to medical care for transgender Americans. This case, too, has been assigned to Judge O’Connor.