WASHINGTON (AP) — Rahm Emanuel’s chances of landing a top Cabinet post in Joe Biden's administration appear increasingly unlikely after the former Chicago mayor emerged as a source of controversy for the president-elect, who had been considering Emanuel for transportation secretary, a person familiar with the matter told The Associated Press.

Emanuel, among multiple candidates in the running for the Cabinet position, appeared to slip down the list in the last two weeks after progressive leaders, including Rep. Alexandria Ocasio-Cortez of New York, criticized the prospect of nominating him for the post, the person said Thursday. That concern has grown deeper in recent days, particularly after the Rev. Al Sharpton raised similar concerns during a meeting with Biden and other civil rights leaders, the person said.

The person was not authorized to publicly discuss private deliberations and spoke to the AP on the condition of anonymity.

A decision hasn’t been finalized, and the dynamics could shift as Biden builds out his Cabinet with an eye to ensuring diverse leadership in the top ranks of his administration.

Whether Emanuel is ultimately picked could also be affected by other factors as Biden has placed a premium on building out a Cabinet and team of senior advisers from a diverse set of backgrounds, according to people familiar with the transition’s deliberations. The dynamic, perhaps more than progressives' opposition to him, is an important factor in whether Biden eventually asks him to join the administration in a Cabinet role, according to two people familiar with deliberations who spoke on the condition of anonymity.

An announcement on transportation secretary is not believed to be imminent.

Representatives for the Biden transition and for Emanuel declined to comment.

Emanuel, a former congressman who also served as former President Barack Obama’s first White House chief of staff, has been a significant force in Democratic Party politics for much of the last three decades. But progressives and civil rights leaders have been critical of his handling of the high-profile police shooting death of Laquan McDonald, a Black teenager killed by a white officer, during his time as Chicago’s mayor.

Emanuel’s allies have pointed to his extensive work making transportation issues top priorities as Chicago’s mayor, including reviving the city’s public transportation system and overhauling the city’s two worn airports. Emanuel also is credited with making Chicago one of the most bicycle-friendly cities in the country during his time in office.

The allies also have argued that Emanuel’s breadth of experience and knowledge of Congress would make him uniquely positioned to lead the department, which includes the Federal Aviation Administration, the National Highway Traffic Safety Administration, the Federal Railroad Administration and others.

The new secretary would inherit an agency at a time the airline industry has been decimated by the coronavirus pandemic, with many airlines turning to massive job cuts.

The pick would also be responsible for ensuring that priorities that have been pushed for years are carried out, including ensuring railroads across the U.S. implement critical speed control technology, known as positive train control, that federal safety investigators have been pushing for close to five decades. The Associated Press reported in 2017 that crashes that federal officials believed could have been prevented by positive train control led to nearly 300 deaths and thousands of injuries and almost $400 million in property damage.

Emanuel was among a number of candidates being considered for America’s top transportation post, including New York City transit chief and former Federal Railroad Administrator Sarah Feinberg — a major proponent of positive train control in the Obama administration — and ex-New York City transportation commissioner Polly Trottenberg, the person said.

Two other high profile Obama-era alumni were announced Thursday as joining the Biden administration — Denis McDonough as veterans' affairs secretary and Susan Rice to head the Domestic Policy Council.

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Associated Press writer Michael R. Sisak in New York contributed to this report.