WASHINGTON — Not long after President Trump took the oath of office, a busload of women’s health advocates made the first of a series of 860-mile round trips from Las Vegas to the Nevada capital, Carson City. Their mission: to push state legislators to expand insurance coverage for contraception.

It worked. On Saturday, Gov. Brian Sandoval of Nevada, a Republican, signed a measure requiring insurers to cover 12 months of birth control at a time, with no co-payment.

Nevada is not the only state where birth control is suddenly on the legislative agenda. With the future of the Affordable Care Act — former President Barack Obama’s signature health care legislation — in doubt and the Trump administration planning to roll back the act’s mandate that employers cover contraceptives, the battle over birth control is shifting to the states.

Currently, 28 states have some type of “contraceptive equity” law, aimed at making birth control cheaper and more accessible. Many of those measures — including one in Nevada — were adopted in the late 1990s. Mr. Trump’s election has again brought the issue to the fore.