A federal judge on Friday blocked President Donald Trump’s attempt to overhaul elections in the U.S., siding with a group of Democratic state attorneys general who challenged the effort as unconstitutional.

Trump’s March 25 executive order sought to compel officials to require documentary proof of citizenship for everyone registering to vote for federal elections, accept only mailed ballots received by Election Day and condition federal election grant funding on states adhering to the new ballot deadline.

The group of attorneys general said the directive “usurps the States’ constitutional power and seeks to amend election law by fiat.” The White House has defended the order as “standing up for free, fair and honest elections” and called proof of citizenship a “commonsense” requirement.

Judge Denise J. Casper of the U.S. District Court in Massachusetts said in Friday’s order that the states had a likelihood of success as to their legal challenges.