It is time for progressives to embrace federalism and to use Supreme Court precedents protecting states’ rights to fight against Trump administration policies. Throughout American history, “states’ rights” have been used by conservatives to oppose progressive change. In the early 19th century, those opposing abolition of slavery did so in the name of states’ rights. In the late 19th and early 20th centuries, the Supreme Court struck down many progressive federal laws, including the first federal statute restricting the use of child labor, on federalism grounds. In the 1950s and 1960s, Southerners opposed desegregation by invoking states’ rights. In more recent decades, the Supreme Court, in a series of ideologically split 5-4 decisions, used federalism to strike down desirable federal laws, including provisions of the Violence Against Women Act, the Brady Handgun Control Act, and the Patient Protection and Affordable Care Act.

But now, with the Trump administration taking far right positions on almost every issue, state and local governments are a key hope. For example, President Donald Trump’s threat to withhold federal funds from “sanctuary cities” is coercion of local governments that violates principles of federalism long advocated by the conservative justices on the Supreme Court.

A great deal of confusion exists over what it means for a city to declare itself to be a “sanctuary.” It does not mean that a city will conceal or shelter undocumented immigrants from detection. Instead, when a city says that it is a “sanctuary,” it means that the city will not be an arm of federal immigration authorities. For example, a sanctuary city will not investigate, arrest, or detain individuals on the basis of immigration status. Rather, the city will provide services to all, regardless of immigration status, and generally will not turn over undocumented individuals to federal immigration authorities.

There are compelling reasons for cities to adopt such policies. Victims of crime and witnesses to crime will not come forward to the police if they fear deportation. Public health officials worry that sick people, including those with communicable diseases, will not go for treatment if they fear that it could lead to their deportation. Of course, their untreated communicable diseases can spread to all of us. Education officials worry that parents will not send their children to school if they think it might lead to deportation. Educating children, whether documented or undocumented, is a moral obligation and obviously essential for society.

Nonetheless, President Trump issued an executive order on January 25, 2017, which threatens sanctuary cities with loss of federal funds. But this violates the Tenth Amendment. The Supreme Court has held that it is unconstitutional for Congress to commandeer state and local governments and force them to administer federal mandates.

For example, in United States v. Printz, in 1997, the Supreme Court declared unconstitutional a provision of the federal Brady Handgun Control Act that required that state and local governments do background checks before issuing permits for firearms. The Court, in an opinion by Justice Scalia, said that such coercion violated principles of federalism and the Tenth Amendment.

Nor may Congress do this by putting strings on grants to state and local governments. The Supreme Court has said that such strings are constitutional only if the conditions are clearly stated, relate to the purpose of the program, and are not unduly coercive. None of these requirements are met by the Trump Executive Order. No federal statute conditions federal funds on cities denying themselves sanctuary status. And most federal grants to local governments have nothing to do with immigration.

But most of all, the Trump Executive Order is impermissibly coercive. In 2012, in National Federation of Independent Businesses v. Sebelius, the Supreme Court, 7-2, declared unconstitutional the Medicaid provisions of the Patient Protection and Affordable Care Act. These provided that if a state accepted federal Medicaid funds, it had to provide coverage for those within 133% of the federal poverty level. The federal government paid 100% of these costs until 2019 and 90% thereafter. The Court, in an opinion by Chief Justice Roberts, declared this unconstitutional as impermissibly coercing state governments in violation of the Tenth Amendment. The Court referred to this as like “a gun to the head” of the states and as “dragooning” them. The Trump Executive Order does exactly the same thing.

The federal government can use its agencies and agents to enforce federal immigration law however it chooses. But it cannot turn local governments into enforcement arms of the federal government. That is exactly what the Trump Executive Order does.

This is just one of many examples where principles of federalism must be used by progressives. In the area of environmental law, it will be crucial for state governments to adopt stricter pollution control laws in the face of the dismantling of federal environmental protections. Just last week, Scott Pruitt, the head of the Environmental Protection Agency, once more denied any link between greenhouse gas emissions and climate change. It is clear that he and the Trump administration will gut federal environmental regulations. But there long has been a principle that states can have stricter environmental laws, so long as Congress does not explicitly preempt this.

Another important area concerns decriminalization of marijuana. A number of states, including California, have repealed laws that make it a crime to possess small amounts of this drug. Attorney General Jeff Sessions has expressed opposition to these laws. But Congress cannot force state governments to enact or enforce laws. A state does not need to have any law prohibiting marijuana, or can have one with exceptions for possession for medical use or for small amounts. To be sure, the federal government can enforce its own drug laws however it wants, but it cannot compel state governments to do so.

States, of course, will vary enormously in their policies. But that, too, is what federalism and states’ rights are about. Progressives should not be hesitant to use conservative decisions to achieve desirable results. We will need all the tools we can find to fight over the next four years.