CHICAGO — An Illinois appeals court panel has ruled that Rahm Emanuel, the former White House chief of staff, does not qualify to run for mayor of Chicago in next month’s election.

The ruling, which was announced on Monday, comes as a significant and unexpected setback for Mr. Emanuel, who has been a front-runner both in polls and in fundraising in the race to replace Richard M. Daley, the city’s longest serving mayor, who will retire this spring.

The question of Mr. Emanuel’s residency — and whether he had lived in Chicago long enough to appear on the city’s ballot — had been a matter of debate since Mr. Emanuel departed the White House last fall to run for mayor.

DEVELOPING….

THE CAUCUS