For decades, California has been able to fund a sprawling administration whose agencies have federal-size budgets and wide latitude to set and enforce rules. But as the nation has fractured along cultural and economic lines, Republican governors, like Greg Abbott of Texas and Ron DeSantis of Florida, have sought to experiment with legislative activism of their own — a kind of anti-California effect. Recently, a number of red states have tried to create conservative guidelines for textbooks, explored ways of preventing companies from paying for employees’ abortions, tried to stop (or at least slow) the move away from fossil fuels and sought to limit Medicaid patients’ access to gender-transition care.

Newsom wants California to aggressively meet this new challenge. Aides to the governor say he often shows up to morning meetings fuming about some new bill signed by a Republican governor, seeking ideas for how to counter. When Texas passed a law allowing private citizens to sue abortion doctors, Newsom used it as a model for legislation that would allow Californians to sue manufacturers of illegal guns. When Walgreens announced that it would not sell mifepristone, an abortion medication, in certain states, Newsom responded on Twitter, writing that California would try to end a contract with the pharmacy.

What Newsom aspires to is a whole new kind of California effect, one that goes way beyond environmental and consumer regulations — regulations that, even though they had national impact, were first and foremost about improving life for California residents. This fight is purely about changing behavior beyond the borders of his state. Newsom describes the gun law as his “first foray” into this area, promising that he is “barely winding up.” If companies accede to Republican demands to deny abortion coverage or curb diversity and clean-energy efforts, he warns, they should expect to pay a financial price in California. “All these corporations, they’re silent, they’re complicit in all of this,” Newsom says. “In the spirit of Reagan, it’s a time for choosing.”

The California effect began with smog. In 1972, Mary Nichols was a young environmental lawyer driving through the haze to a Los Angeles courthouse, where she hoped a legal victory would help improve the region’s air pollution. Two years earlier, Congress passed the Clean Air Act, and Nichols’s firm was arguing that the law required the E.P.A. to compel California to create a plan to solve the smog problem — in other words, that it was the federal government’s responsibility to push the state to act. The case was ultimately successful, and it was the start of Nichols’s career as one of the auto industry’s most powerful regulators. From her perch on the West Coast, she would spend the next five decades doing the reverse: Instead of using the federal government to change California, she would use California to change the nation.

Seven years after the Clean Air Act lawsuit, Gov. Jerry Brown appointed Nichols to be chairwoman of the California Air Resources Board (CARB), a pollution agency created in 1967. Around that time, Congress, in response to the demands of the influential California delegation, gave the state a powerful regulatory tool: a waiver that allowed California, and only California, to set air-quality standards higher than the federal government’s. The auto industry lobbied fiercely against the waiver, worried that California would use it to determine policy for the whole country, which of course it did: As CARB forced carmakers to reduce particulate matter and toxins like nitrogen oxides and ozone, the rules Nichols put in place became the national standard.