President Donald Trump’s request to add a documentary proof of citizenship requirement to the federal voter registration form cannot be enforced, a federal judge ruled Friday.

US District Judge Colleen Kollar-Kotelly in Washington, DC, sided with Democratic and civil rights groups that sued the Trump administration over a March executive order to overhaul US elections.

She ruled that the proof-of-citizenship directive is an unconstitutional violation of the separation of powers, dealing a blow to the administration and its allies who have argued that such a mandate is necessary to restore public confidence that only Americans are voting in US elections.

“Because our Constitution assigns responsibility for election regulation to the States and to Congress, this Court holds that the President lacks the authority to direct such changes,” Kollar-Kotelly wrote in her opinion.

She further emphasized that on matters related to setting qualifications for voting and regulating federal election procedures, “the Constitution assigns no direct role to the President in either domain.”

Kollar-Kotelly echoed comments she made when she granted a preliminary injunction over the issue.

The ruling grants the plaintiffs a partial summary judgment that prohibits the proof-of-citizenship requirement from going into effect. It says the US Election Assistance Commission, which has been considering adding the requirement to the federal voter form, is permanently barred from taking action to do so.

In a statement, Sophia Lin Lakin of the ACLU, one of the plaintiffs in the case, called the ruling “a clear victory for our democracy. President Trump’s attempt to impose a documentary proof of citizenship requirement on the federal voter registration form is an unconstitutional power grab.”

A message seeking comment from the White House was not immediately returned.

While a top priority for Republicans, attempts to implement documentary proof-of-citizenship requirements for voting have been fraught. The US House passed a citizenship mandate last spring that has stalled in the Senate, and several attempts to pass similar legislation in the states have proved equally difficult.

Such requirements have created problems and confusion for voters when they have taken effect at the state level. It presents particular hurdles for married women who have changed their name, since they might need to show birth certificates and marriage certificates as well as state IDs. Those complications arose earlier this year when a proof-of-citizenship requirement took effect for the first time during local elections in New Hampshire.

In Kansas, a proof-of-citizenship requirement that was in effect for three years created chaos before it was overturned in federal court. Some 30,000 otherwise eligible people were prevented from registering to vote.

Voting by noncitizens also has been shown to be rare.

The lawsuit brought by the DNC and various civil rights groups will continue to play out to allow the judge to consider other challenges to Trump’s order. That includes a requirement that all mailed ballots be received, rather than just postmarked, by Election Day.

Other lawsuits against Trump’s election executive order are ongoing.

In early April, 19 Democratic state attorneys general asked a separate federal court to reject Trump’s executive order. Washington and Oregon, where virtually all voting is done with mailed ballots, followed with their own lawsuit against the order. (CNN)