The request to drop the case came days after Republicans suffered significant losses in the midterm elections and about a week before a scheduled hearing where a special master was set to evaluate the accuracy of the government's list. California officials have said the list is out of date and includes legitimate voters — a view echoed by the federal judge presiding over the case in a sharply worded order denying the government's request.

The case had been at the forefront of President Donald Trump's administration's effort to assert control over state-run elections across the country, which Trump has said are rife with illegal voting without providing evidence.

In its motion to dismiss, the department said that by the time of the upcoming hearing, the state would have already irreparably "commingled the challenged ballots with lawful ones."

"The relief the United States sought and needed is no longer available—rendering voluntary dismissal necessary," the motion said.

Bill Essayli, the top federal prosecutor in Los Angeles, previously argued in court that the lawsuit would be irrelevant after election day because there would be no way to sequester the ballots allegedly belonging to noncitizens. The lawsuit was filed in mid-October, when ballots had been sent to all of the state's 23 million registered voters and after hundreds of thousands of ballots were already processed. Once a ballot is processed, it is completely anonymized.

Essayli said at the time the lawsuit was filed that his goal was to "safeguard the integrity of the election so it doesn't have an effect on the upcoming election."

"We want to stop the illegal voting. We don't want to chase it later," he said outside of court the week before the election.

U.S. District Judge David O. Carter appointed the special master in late October, shortly after allowing California to proceed with elections as planned. Carter, who was appointed by former President Bill Clinton, argued in his order that separating ballots at that late stage would risk disenfranchising citizens and warned it would "wreak havoc" on the midterm elections. The special master would have also considered whether California election officials did in fact have a mechanism for separating the ballots.

California had processed roughly 9 million ballots as of early Friday, with nearly 5 million still left to be counted, according to state election officials.

The Department of Justice remains enmeshed in litigation with multiple immigrant and voting rights groups seeking to limit its use of the list of what it says are suspected noncitizens. Another controversial suit it filed in Alaska at Trump's direction before the election to block the victory of the Democrat in that state's Senate race was swiftly dismissed by a federal judge. The administration is appealing that ruling but has yet to file a full brief at the 9th Circuit Court of Appeals.

California prosecutors in recent weeks have arrested over 30 noncitizens accused of illegally registering to vote. Some of those arrested were also accused of voting in previous elections. Elections clerks around California in the week before the election were sent subpoenas to testify before grand juries slated to convene in November. It is not clear who is being criminally charged in those cases, but the department does not typically subpoena people whom it regards as targets of a criminal investigation to appear before a grand jury.

The dismissal marks a retreat for an administration that had made election oversight a central priority, and it leaves California's vote-counting process to proceed without federal court intervention as the state continues to tally millions of remaining ballots.