The judge's order, in a high-profile case about vote-by-mail in the battleground state, essentially forces the Trump campaign
to try to back up President Donald Trump's false claims about massive voter fraud in postal voting.
"The Court finds that instances of voter fraud are relevant to the claims and defenses in this case," District Judge J. Nicholas Ranjan wrote on Thursday, telling Republicans that they need to provide evidence of fraud to the Democratic Party and the Sierra Club, which are part of the lawsuit.
The Democrats had asked for information and documents that would show steps the Republicans took to study the possibility of fraud, especially related to the use of dropboxes, ballot collection and mailed-in ballots in the primary elections.
The Trump campaign and Republicans had refused to do so. But with Thursday's court order, they must answer questions from the Democratic groups and turn over records of communications -- or say they have none. The Trump campaign has until Friday to respond, the judge said.
The Trump campaign "should not be permitted to raise such spectacular fraud related claims, particular in this national climate," lawyers representing the Democrats wrote.
The Democrats have called the Trump lawsuit an attempt to stoke fears about unproven fraud related to mail-in voting in the battleground state. Trump has repeatedly claimed there is massive voter fraud -- something that CNN's fact-checking team has repeatedly debunked.
Legal scholars from both parties, and nonpartisan experts, acknowledge that there is no widespread fraud in US elections.
The case is one of the boldest attempts by the Trump campaign in court to curtail mail-in voting in the 2020 election. The Trump campaign had claimed mail-in voting could prompt questions about the accuracy of election results "and ultimately chaos," according to the court record.
Ranjan, the judge overseeing the suit, was appointed by Trump.
A hearing about the evidence is set for late September.