John Yoo and Jesse Choper quoted by California Magazine, Feb. 7, 2018
Yoo: “States don’t have the power to interfere with federal operation. … If the state is trying to prevent people from obeying federal law, they might be committing obstruction of justice—which is a crime.”
Choper: “For California to pass a law to regulate private citizens, telling them that if they follow federal law they’re in violation of state law—that is very different than the state simply saying, ‘We’re not going to enforce [the federal government’s] law. If you want to [enforce] it, do it yourself.’ That’s a major step that I do not think is within the state’s power.”