The initial efforts by the conservative movement to deploy transgender issues did not go well. In 2016, North Carolina legislators voted to bar transgender people from using the bathroom of their preference. It created a backlash so harsh — from corporations, sports teams and even Bruce Springsteen — that lawmakers eventually rescinded the bill.

As a result, conservatives went looking for a new approach to the issue. Mr. Schilling’s organization, for instance, conducted polling to determine whether curbing transgender rights had resonance with voters — and, if they did, the best way for candidates to talk about it. In 2019, the group’s research found that voters were significantly more likely to support a Republican candidate who favored a ban on transgender girls participating in school sports — particularly when framed as a question of whether “to allow men and boys to compete against women and girls” — than a candidate pushing for a ban on transgender people using a bathroom of their choosing.

With that evidence in hand, and transgender athletes gaining attention, particularly in right-wing media, conservatives decided to focus on two main fronts: legislation that addressed participation in sports and laws curtailing the access of minors to medical transition treatments.

In March 2020, Idaho became the first state to bar transgender girls from participating in girls’ and women’s sports, with a bill supporters in the Republican-controlled legislature called the “Fairness in Women’s Sports Act.”

A burst of state legislation began the next year after Democrats took control of Congress and the White House, ending four years in which social conservatives successfully pushed the Trump administration to enact restrictions through executive orders.