President Donald Trump on Monday vowed to end birthright citizenship, and California Attorney General Rob Bonta says he and the state are prepared to fight back. On Inauguration Day, Trump signed an executive order saying in effect children born in the United States to parents who did not enter the country legally can be denied citizenship. Bonta on Tuesday responded. The state attorney general along with San Francisco City Attorney David Chiu filed a lawsuit and motion for preliminary injunction to immediately block Trump’s executive order seeking to end birthright citizenship. “As home to more immigrants than any other state in the country, California has a vested interest in ensuring that the federal government recognizes the fundamental rights of the children of immigrants who are born in our state,” Bonta said. “As he so often did in his first term in office, the president once again overstepped his authority with this unconstitutional executive order.” Bonta is not the only state attorney general promising to fight. And the ACLU filed a lawsuit hours after the order. Meanwhile, protesters in San Jose gathered to decry that order and nine others related to immigration, incuding declaring a national emergency at the U.S.–Mexico border as well as immigration enforcement action in major cities. The birthright citizenship issue dates back to the Civil War, and one of the biggest court challenges was posed by a San Francisco man whose parents were born in China. In that 1898 case, the court ruled that because he was born in San Francisco, he was a U.S. citizen.