State and local governments could be a roadblock for some of Trump's more radical policies

President-elect Donald Trump and his allies have vowed to radically shift American policy from Day 1.

From mass deportations to eliminating the Department of Education, Trump's policies could impact millions of people and communities across the country. However, experts say there is a big obstacle that will make it harder -- if not impossible -- for the incoming administration to implement these plans: States and municipalities.

Alison LaCroix, professor of constitutional law at the University of Chicago Law School, told ABC News that the power to regulate and implement key laws lies strictly within the states and many local leaders have already been working to prepare for a possible future Trump administration.

"The states have a lot of levers in the constitutional system, legal system and other systems," she said. "This usually comes as a lot of shock to people who don't know how much power they wield but we're going to soon find out how valuable they are."

Other experts who have focused on some of the biggest sectors targeted by Trump, such as public health and immigration, agreed but said they are likely gearing up for a legal and policy fight that could last a long time.

Immigration

For example, Trump and his allies have been very open about their proposals to deport millions of undocumented immigrants.

Trump has said he aims to remove at least 1 million immigrants living in the country illegally from the U.S. as soon as possible.

Elora Mukherjee, the director of Columbia Law School's immigration clinic, told ABC News that states can't outright act as immigration enforcement for the federal government without an agreement.

"It is the principle that the federal government cannot order local law enforcement to enact federal priorities," she said.

Democratic governors like Gavin Newsom of California and JB Pritzker of Illinois have vowed not to assist Trump with any mass deportation plan, and Mukherjee said their claims are not empty words.

She said states already showed their power during the first Trump administration by blocking Immigration and Customs Enforcement agents from entering courthouses for potential raids and denying the agency detainers that would have kept jailed immigrants in custody longer without an arraignment.

She added that any attempts by the Republican-controlled Congress to change immigration and deportation laws to take away rights from the states will take some time and likely be met with resistance even among Republican members who think it is too extreme.

"The Trump administration will issue many executive orders, but a large number that will be illegal and unconstitutional," Mukherjee added.

At the same time, Mukherjee said that conservative states and municipalities may bolster anti-immigrant policies and make it harder for migrants and asylum seekers to gain a path to citizenship.

Sixty counties and police districts, many of them in Florida, have entered into 287(g) agreements with ICE, in which local law enforcement can conduct immigration policies on behalf of the federal government such as executing warrants and detaining undocumented immigrants, according to Mukherjee.

Florida also passed SB 1718 last year which cracks down on undocumented immigration with several provisions, including making it illegal to transport undocumented immigrants and requiring hospitals to ask patients for their immigration status.

Mukherjee stressed that states cannot try to enforce their own laws in other jurisdictions due to the 1842 Supreme Court case Prigg vs. Pennsylvania. That case, which overturned the conviction of a man convicted under a state law that prevented slave-catching, held that while federal law supersedes state law, states are not required to use their resources to uphold federal laws.

"It's extremely difficult and illegal for one state to impose their laws onto another," Mukherjee said.

Even when it comes to executive orders, Mukherjee said the laws are mostly on the side of states and municipalities.

Trump’s "border czar" choice Tom Homan has already threatened to go after states and cities that refuse to comply with the president-elect's deportation plans, including arresting mayors.

Mukherjee said there is no legal mechanism or modern legal precedent that allows the federal government to incarcerate local leaders for not adhering to an administration's policy.

"Sanctuary city laws are entirely allowed within the U.S. Constitution," she said. "The 10th Amendment is extremely clear. The powers not given to the federal government are reserved to the states or the people. This is a bedrock principle of U.S. constitutional law."

Public education

State education officials are in the same boat when it comes to federal oversight, experts said.

Although Trump and other allies have made it clear that they want to eliminate or weaken the federal Department of Education, funding for schools and education programs lies mostly in the hands of state legislatures and local school boards, according to Alice O'Brien, the general counsel for the National Education Association.

"Those campaign promises in reality are much harder to achieve," O'Brien told ABC News. "They would require federal legislation to accomplish."

Federal oversight has little control over local school curriculum policies, she added.

O'Brien noted that much of the federal oversight on public schools lies outside of the jurisdiction of the Department of Education. For example, state school districts must adhere to laws set forth at the federal level such as non-discrimination against race and religion and disabilities.

"States and school systems can not run in any way that conflicts with the federal Constitution," O'Brien said.

When it comes to funding, although the federal DOE does provide funding as a floor to many school districts, it is a small fraction compared to the funding that comes from city and state coffers, O'Brien explained.

Public health

"It really comes down to a state-by-state basis in terms of how much dollars are allocated to the schools," she said. "Ultimately it really comes down to how much money the state budgets have."

Dr. Georges C. Benjamin, the executive director of the American Public Health Association and former Maryland health secretary, told ABC News that state public health offices operate under the same localized jurisdiction and thus would have more autonomy on health policies.

Trump's pick for the head of Health and Human Services, Robert F. Kennedy Jr., has been a staunch promoter of anti-vaccination policies and has pushed for the end of fluoride in water supplies.

Benjamin said he is worried about the effects of having someone with no professional health experience and public dismissiveness of proven health policies, however, he remarked that states and municipalities still hold immense power in implementing policies.

Georges noted that fluoride levels in the water supply are dictated at a local level, and many counties have chosen not to implement them. Federal health agencies can make recommendations but cannot block a municipality from implementing fluoridation, he said.

"There is no fiscal penalty for not following it," Benjamin said of federal recommendations.

The same rules govern local vaccination requirements, he added.

"[The federal government does] control vaccine mandates at the federal level, with the federal workforce, but they don't control the bulk of childhood mandates," Benjamin said.

He noted that the country saw the effectiveness and ineffectiveness of state-run public health systems during the two years that COVID-19 hit the nation and the rollout of the vaccines. Republican and Democratic states all instituted shelter-in-place and social distancing rules during the peak of cases, Benjamin said.

"I do think we have a wait-and-see attitude," he said.

In the meantime, several states have taken measures to bolster their state health policies, particularly when it comes to reproductive rights, through legislative action and ballot measures.

Power in state prosecutors

One of the biggest ways that states will be able to "Trump-proof" their laws and policies is through state prosecutors and the courts, LaCroix said.

"We will see a lot of arguments in local government and what they can do," she said.

Mukherjee said several state attorneys general were able to take Trump to court during his first administration and push back against immigration proposals such as his ban on residents from Muslim countries and deportation plans.

Mukherjee said despite the increase in Trump-backed judges in the federal courts, there is still the rule of law when it comes to immigration. For example, earlier this year, a federal judge struck down the provision in Florida's SB 1718 that threatens felony charges for people who transport an undocumented immigrant.

U.S. District Judge Roy Altman, a Trump-appointed judge, issued an injunction against that provision stating that immigration-related enforcement was not in the state's power.

"It will be harder this time around to win sweeping victories for immigrants and non-citizens ... but federal judges across party lines reined in the worst abuses of the Trump administration the first time around," she said.

LaCroix echoed that statement and said that partisanship can only go so far, especially when it comes to laws enshrined in the state and federal constitutions.

"Judges still have to give reasons for what they do and 'because our party is in charge' doesn't hold weight," she said.