A federal judge has rejected a Trump administration request to stop California from processing the ballots of up to 20,000 people, warning it would "wreak havoc" on the midterm elections.

Wednesday's ruling by U.S. District Judge David O. Carter comes as more than 3. 7 million people have already voted in the state.

The decision is the latest legal setback for President Donald Trump in his efforts to expand federal control over state-run elections ahead of voting that will decide control of Congress for the rest of his term.