What does it mean to be a resident of a city?
If history unfolded differently, and Abraham Lincoln had served out his second term in the White House, could he have returned to Illinois to run for mayor of his hometown?
The response might have boiled down to this: Honest, Abe, you can't, unless you've lived in Springfield for a full year.
That's the issue hanging over Rahm Emanuel's run for Chicago mayor. And it's raising tough questions about how old residency rules should be interpreted in an era when Americans are so mobile.
The Illinois laws governing municipal elections are not unlike similar laws around the country. But the unusually strict interpretation by an appellate court this week would pose difficulties for many prospective officeholders whose careers take them for a time to Washington or to other countries.
The court on Monday threw Emanuel off the Chicago ballot, saying he could not run because he had been living for two years in Washington, where he was the White House chief of staff. Emanuel has appealed that decision to the Illinois Supreme Court.
But the same problem could arise for Education Secretary Arne Duncan, who once headed Chicago schools, or Emanuel's White House successor, Bill Daley, another Chicago native.
If Duncan wanted to run for mayor, "he's out under this," said Michael Dorf, a Chicago attorney and election law expert. "If Lincoln wanted to run for mayor of Springfield, sorry Abe."
Residency laws vary across the nation. To be mayor of New York, candidates just have to live in the city on the day they are elected. In other states, some office seekers must have been residents for five years.
But the appellate court in Illinois departed this week from most previous interpretations of election law when it said Emanuel needed to be physically present in Chicago for at least a year prior to the election, regardless of why he left or whether he intended to return.
Dawn Clark Netsch, a prominent Chicago Democrat who now teaches law at Northwestern University, said the appellate ruling would stop even Chicago's most prominent political alum, President Barack Obama.
"Obama has not been physically present in Chicago," said Netsch. The court's new rationale, she added, had "never been thought of before."
The law states that a person is ineligible for an elected city office unless that person is a qualified voter in that city "and has resided in the municipality at least one year next preceding the election or appointment."
In the past, if candidates moved away, they could demonstrate an intention to return by leaving their voter registration and driver's license unchanged and keeping a home in the area — all of which Emanuel said he did.
Experts say a court has never simply ignored a candidate's intent.
"We've all been working under this absolute presumption based on cases of the last 50 years that intent was really the key," Dorf said. "But the appellate court got rid of intent totally."
Edward Foley, a law professor at Ohio State University who heads the school's election law program, said the court's decision to disregard intent was striking.
"There is a general theme in election law that when in doubt, you err on the side of democracy," he said. "If there is any doubt about the understanding of the statute, you interpret it so that you let the voters decide."
Both the Illinois election code and the municipal code leave some questions unanswered.
The municipal code, for example, says people who have been away serving in the military cannot be disqualified from running for office. And a person does not lose residency if he or she is "on the business of the United States."
But, Dorf said, the court concluded that applied to voting, not seeking office.
And, he said, while the state's municipal code specifically says candidates must be residents of the city for 12 months, it does not define that, or say how many days in those 12 months a person must be in the city. Nor does it say if steps like maintaining one's voter registration are enough to demonstrate residency.
Appellate Justice Bertina Lampkin made the same point in her dissent of the 2-1 opinion, blasting fellow justices for not including "a single sentence" to explain what constitutes actual residency when discussing Emanuel's absence from Chicago.
"How many days may a person stay away from his home before the majority would decide he no longer 'actually resides' in it?" Lampkin wondered. "Would the majority have us pick a number out of a hat?"
Also unclear is just how many other municipal posts might be affected.
The election code does not list the jobs that might be considered the "business of the United States," but experts say it could include a tour in the Peace Corps, a job with a congressman in Washington or other government positions.
The Illinois law stands in stark contrast to federal law, which allows candidates to run for Congress without establishing residency — including in Illinois, where Maryland resident Alan Keyes was drafted to be the Republican Senate nominee against Obama in 2004, after the original candidate dropped out.
"About the only time Keyes spent in Chicago was changing planes at O'Hare," said Kent Redfield, a professor emeritus of politics at the University of Illinois-Springfield.
If the appellate decision stands and Emanuel is cast out of the race, questions will linger about the wisdom of his decision to rent out his Chicago house instead of continuing to have his family live there. What if he had left it vacant so he could stay there whenever he returned to the city?
Dorf said he expects the Supreme Court to reverse the appellate decision.
If that doesn't happen, the effects will extend far beyond the circumstances of a White House aide who hustled back to the city when Mayor Richard Daley made his stunning announcement that he would not seek a seventh term.
"I think it creates a financial test for being able to run for office to the extent that if you can't afford to leave your place vacant for two years . you can't run," he said.
Andrew Finko understands all that. But Finko, an attorney who represented two people challenging Emanuel's residency, said the law clearly states that anyone who has not lived in the city for a full year before election day cannot run for mayor.
"You have to make your choices and you have to live with them," he said. "If you decide to go to Washington, that's your choice. You can't do everything."