The Trump administration’s aggressive policies on immigration are receiving pushback not just on Capitol Hill but across the country. Democratic leaders in multiple states are refusing to cooperate with immigration arrests.

In response, the federal government is refusing to share evidence with state investigators in the deaths of Renee Good and Alex Pretti, who were killed by federal officers while protesting immigration enforcement in Minneapolis.

Throughout U.S. history, there have been many moments of conflict between the federal and state governments, such as on slavery, racial segregation, school testing requirements, health care, abortion and climate change. Conversely, there has also been a long history of cooperation between the different levels of government in matters such as disaster relief, law enforcement and antiterrorism efforts.

But what happens when the various states and the federal government see the same legal issue differently? Which side wins in a dispute? This is an ongoing and open question, as evidenced by the frequent lawsuits being filed against Trump administration policies by state attorneys general.

As a legal scholar, I study issues related to constitutional law, including federalism, or the division of power between the various levels of government in the U.S. system. Ultimately, the question of who prevails when there’s a dispute depends on whether the issue is more national or local in scope. It may also matter whether the issue affects fundamental rights, which no government may justly infringe.

The framers of the Constitution saw the division of power between the states and federal government as part of the U.S. system of checks and balances. Just as the judicial, executive and legislative branches check each other, so do the different levels of government. “The true barriers of our liberty in this country are our state governments,” Thomas Jefferson wrote in 1811.

Still, it’s easy to assume that the federal government has greater power. The U.S. Constitution states that federal laws are “the supreme Law of the Land.” This is a model known as vertical federalism – in essence, putting the federal government above the states and localities.

There are areas of law where that framework clearly prevails. For example, immigration is an issue that the Constitution places squarely under the authority of the federal government. States cannot nullify, or invalidate, federal law. That is vertical federalism.

But the 10th Amendment says “powers not delegated to the United States … are reserved to the States respectively.” There are areas where states retain authority and the relationship between the levels of government is more horizontal, or flat or equal.

Consider cannabis. In 1996, California voters approved a ballot initiative making their state the first to allow the medical use of marijuana since prohibition started in the early 1900s. This was despite the fact that federal law viewed all cannabis as contraband. But California determines its own criminal code.

Californians could not stop the federal government from enforcing a valid federal law in their state, but that did not mean that California – or the vast majority of other states that have since passed their own medical or recreational marijuana measures – have to participate in a federal policy choice.

Federal agencies have continued occasional cannabis raids in California. But for state law enforcement officials, failing to punish a person for the medical use of cannabis is not a federal crime. In 1997, the Supreme Court ruled that the federal government cannot force a state “to enact or enforce a federal regulatory program.” That is horizontal federalism.

The federal government is limited to its enumerated powers – which is to say, the powers spelled out directly by the U.S. Constitution. But states possess “police powers,” which is a broader authority to regulate health, safety and morality.

The federal government is responsible for foreign policy and regulating interstate commerce. But states and localities regulate vaccine mandates, police and fire services, and operate or oversee water and sewer systems, as well as taking stances on moral issues, including alcohol and gambling, due to their potential to cause harm.

But both the federal government and the states are limited by the Constitution. Neither can justly violate the freedom of the press, for example, under the First Amendment.

And the reality is that, at least at this point in history, there is no neat division between federal and state authority on a broad range of issues. The federal government, for example, pays for the bulk of interstate highway construction. But those roads are actually paved by states.

When the federal government is paying a share of the cost of carrying out its policies, the Supreme Court has ruled that it can, in fact, tell states what to do, such as enforcing a legal drinking age of 21 or risk a share of federal highway funds. But it has also found that federal demands on states can be unconstitutionally excessive or “coercive,” as with a mandate under the Affordable Care Act to expand Medicaid, which the court struck down, even though Washington was paying most of the bill.

Federalism and the question of which level of government has the ultimate say is often complex and messy. But for that reason, as the framers foresaw, it remains an important safeguard of liberty, preventing too much power from residing in one place.

This article is republished from The Conversation, a nonprofit, independent news organization bringing you facts and trustworthy analysis to help you make sense of our complex world. It was written by: Kenneth Michael White, Kennesaw State University

Read more:
Minneapolis united when federal immigration operations surged – reflecting a long tradition of mutual aid

Abortion laws show that public policy doesn’t always line up with public opinion

The legal limits of Trump’s crackdown on sanctuary cities like Philadelphia

Kenneth Michael White does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.