DES MOINES, Iowa (AP) — The federal government has long had sole authority over immigration policy in the United States, but several Republican-led states have continued to push for a role in enforcing regulations out of frustration with current policy and as a way to criticize Democratic U.S. President Joe Biden.

With polling showing Americans are increasingly worried about illegal immigration, the concern has become a top issue in the presidential campaign between Biden and Republican Donald Trump. Republican officials in several states say they owe it to their citizens to be more proactive in charging and deporting people who don’t have legal status to be in the U.S.

Iowa is among states that have approved laws granting state law enforcement and courts the right to file criminal charges against people based on their immigration status, but this week a federal judge blocked the state’s new regulations that were set to take effect July 1.

What happened in Iowa?

A federal judge on Monday issued a preliminary injunction that blocks a law approved by Republican lawmakers and GOP Gov. Kim Reynolds that gave state authorities some power that has been left to federal officials. The Iowa law would allow prosecutors to file criminal charges against people who have outstanding deportation orders or who previously have been removed from or denied admission to the U.S.

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After being arrested, migrants would have a choice of agreeing to a judge’s order to leave the country or being prosecuted, potentially facing time in prison before deportation.

The U.S. Department of Justice and a coalition of civil rights groups filed a lawsuit that argued Iowa’s new rules would lead to confusion and chaos. In his ruling, U.S. District Court Judge Stephen Locher temporarily blocked the law, saying the DOJ and civil rights groups would likely succeed in their argument that federal immigration law preempted the new Iowa law.

Locher said the law might be “defensible” as a matter of politics but “as a matter of constitutional law, it is not.”

Iowa’s Republican Attorney General, Brenna Bird, criticized the Biden administration for seeking to block the state’s law and promised to appeal.

What other states are passing immigration laws?

Texas has taken the lead in seeking a state role in immigration law enforcement, passing a law under which migrants who are in custody on illegal entry charges can abide by a judge’s order to leave the country or face prosecution. The law was in effect for only a few hours in March before a three-judge federal appeals court put it on hold.

The DOJ has sued Oklahoma to block a similar law, arguing it violates the U.S. Constitution.

In Georgia, a new law requires jail officials to check with U.S. Immigration and Customs Enforcement to determine whether prisoners are known to be in the country illegally. The law makes it a misdemeanor to knowingly fail to check immigration status and denies state funding to local governments that don’t cooperate.

Tennessee Gov. Bill Lee has signed into law a bill that requires law enforcement agencies to communicate to federal authorities if they know of people in the country illegally and to help authorities identify, detain and deport them.

New Hampshire lawmakers also approved a proposal aimed at people suspected of entering the country illegally that would make it a crime to cross certain properties that have been preserved as open space unless engaging in permitted activities such as hunting, fishing or hiking. The change to the state’s trespassing law is awaiting the governor’s signature.

Are Democrats passing immigration legislation?

States led by Democrats have largely left immigration enforcement to the Biden administration, but some have sought to expand immigrant rights.

In Maryland, lawmakers approved a bill seeking a federal waiver to let people buy health insurance through the state’s health care exchange, regardless of immigration status.

Arizona Democratic Gov. Katie Hobbs vetoed a bill in March similar to the Texas law, prompting legislators to narrowly approve a measure asking voters to make it a state crime for noncitizens to enter the state at any location other than a point of entry. The measure will go on the Nov. 5 ballot.

Why are politicians focusing on this issue?

Polling shows that more than half of U.S. adults think Biden’s immigration policies have hurt the country.

Trump and other Republicans have sought to benefit from that vulnerability by highlighting asylum-seekers and other migrants seeking to illegally enter the U.S.

Biden and some other Democrats have responded by noting the president proposed strict immigration restrictions but were blocked by Republicans, with the president arguing that Trump wanted to keep the conflict alive as a campaign issue.

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Jeff Amy in Atlanta; Holly Ramer in Concord, New Hampshire; Brian Witte in Annapolis, Maryland; and Jacques Billeaud in Phoenix contributed to this report.