An Illinois state appeals court has thrown the Chicago mayor's race into turmoil by ruling that front-runner and former White House chief of staff Rahm Emanuel did not qualify for the February ballot.
Illinois law requires candidates for municipal offices to be residents of the city for a year prior to elections.
The appellate court, in its 2-1 ruling, said that although Emanuel owned a house in the city, he did not live there.
The ruling overturned decisions by a lower court and a Chicago elections board that had allowed Emanuel to run in the 22 February election.
Mr Emanuel resigned as President Barack Obama's White House chief of staff last year to run for mayor, was challenged on the residency issue by several Chicago residents.
The court said that under Illinois law, an exception for residency while serving on US business is extended to voters, but not to candidates.
A Chicago Tribune poll published last week showed Emanuel leading the race by a comfortable margin, with 44% compared to his nearest rival Braun at 21%.
Emanuel has raised $11.8m (€8.6m) for the campaign, from big names such as film director Steven Spielberg.
Braun has raised less than $500,000 (€336,000).
Dick Simpson, a University of Illinois-Chicago political analyst has said that ' it changes the entire complexion of the race.'
Mr Simpson said that former US Senator Carol Moseley Braun becomes the leading candidate in the race.
Dick Simpson has said he expects Rahm will appeal to the state Supreme Court, an effort which could consume his campaign for several weeks.
