Now, in a case that puts the president in a tough position both personally and politically, Onyango's request is being reconsidered under a little-used provision in U.S. immigration rules that allows denied asylum claims to be reheard if applicants can show that something has changed to make them eligible.
Such as the ascension of her nephew to the presidency of the world's most powerful country.
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"If she goes back to Kenya, she is going to be much more in the limelight, and that, in and of itself, could put her at a greater risk. The chances of her going back and keeping a low profile are gone at this point," said Boston immigration attorney Ilana Greenstein.
Onyango, 56, the half-sister of Obama's late father, moved to the United States in 2000. Her first bid for asylum was rejected, and an immigration judge ordered her deported in 2004; she continues to live in public housing in Boston.
In December, a judge agreed to suspend the deportation order and reopen her case. An initial hearing is scheduled Wednesday in U.S. Immigration Court in Boston.
Obama has said repeatedly that he didn't know his aunt was living in the United States illegally and believes that laws covering the situation should be followed. If she wins asylum, he could look soft on immigration enforcement. If she loses, he could face criticism from immigrant advocacy groups.
The White House says Obama is staying out of it.
"The President believes that the case should run its ordinary course, and neither he nor his representatives have had any involvement," spokesman Ben LaBolt said last week.
Over the past decade, relatively few Kenyans have sought asylum in the United States: 343 through immigration courts in the fiscal year 2008, compared with 9,250 asylum requests from China and 6,424 from El Salvador. Only 60 Kenyans were granted asylum that year through immigration courts.
From the fiscal years 1999 through 2008, about 20 percent of Kenyans who applied through immigration courts were granted asylum, according to an Associated Press review of immigration records.
People who seek asylum must show that they face persecution in their homeland on the basis of religion, race, nationality, political opinion or membership in a social group.
Onyango's reasons for seeking asylum have not been made public, and her immigration hearing will be closed at her lawyer's request.
Kenya has been fractured by violence in recent years. In 2008, more than 1,000 people were killed in the East African nation following a disputed presidential poll, which saw a Luo candidate, Raila Odinga, declared loser to President Mwai Kibaki, a Kikuyu, the largest tribe in Kenya.
Since Kenya gained independence from Britain in 1963, periodic tensions have arisen among the Luos — Onyango's tribe — and some of Kenya's other tribes, including the Kikuyus.
J. Patrick Kelly, an international law professor at Widener University, said the United States views Kenya as fairly stable. The country acts as a regional diplomatic and economic hub and hosts the only headquarters for a United Nations agency outside the West, the U.N. Environment Program.
Onyango could improve her chances of winning asylum if she can argue successfully that some in the Kenyan government may perceive — because of her relationship with Obama — "that she may have some level of political power and be able to transfer that power" to her tribe, Kelly said.
Onyango's lawyer, Margaret Wong, may also argue that she needs to stay in the United States for medical reasons. Onyango, who has been photographed walking with a cane, has some kind of a neurological problem, said Mike Rogers, Wong's spokesman.
In his memoir, "Dreams from My Father: A Story of Race and Inheritance," Obama affectionately referred to Onyango as "Auntie Zeituni" and described meeting her during his 1988 trip to Kenya.
Onyango has not responded to requests for interviews. Her case is being closely watched by people on all sides of the immigration debate. Some critics say her status has already damaged the president's credibility on immigration issues.
"The president's moral authority has been compromised by his aunt's situation," said Dan Stein, president of the Federation for American Immigration Reform. "Americans have the right to expect aliens to respect our law, to leave when they are supposed to and not thumb their nose at the legal system."
But immigrant advocates say opponents are unfairly using Onyango's case as political fodder.
"Whether it's the president's aunt, my aunt or your aunt — anybody who's seeking asylum is seeking that status for a very important reason," said Ali Noorani, executive director of the National Immigration Forum. "We are always worried that a person whose asylum claims are rejected, that they end up in a situation where they are a victim of violence."