WILMINGTON, Del. — President Joe Biden’s choice to head the Federal Aviation Administration has withdrawn his nomination, a setback for the administration that comes after Denver International Airport CEO Phillip Washington appeared to lack enough support in the closely divided Senate.

Transportation Secretary Pete Buttigieg confirmed Washington’s withdrawal in a tweet Saturday night, calling him an «excellent candidate» and blaming undeserved and partisan attacks.

Republicans rallied in opposition to Washington, calling him unqualified due to his limited aviation experience. Democrats and allied independents could still have pushed the nomination, but key senators on their side refused to support choosing Biden.

The fate of Washington seemed decided when the chair of the Senate Commerce Committee, Maria Cantwell, D-Wash., abruptly canceled a scheduled vote last Wednesday, a sign that she lacked enough votes to get the nomination out of the committee. She said some senators wanted more information on Washington.

Sen. Kyrsten Sinema of Arizona, who was a Democrat until she became an independent in December, and moderate Democrat Jon Tester of Montana declined to say how they would have voted. A person familiar with the matter told The Associated Press that Sinema was holding up the nomination and had voiced her opposition. The person was not authorized to discuss the process publicly and insisted on anonymity.

Before the White House announces a new candidate, it will most likely want assurances of support from Sinema, Tester and other moderates.

The FAA has lacked a Senate-confirmed administrator since March 2022. The agency is trying to reassure Americans that air travel is safe despite an increase in close calls between planes this year. It is also struggling with outdated technology that failed in January, briefly canceling all takeoffs across the country. And it’s still trying to repair its reputation after approving Boeing planes that crashed in 2018 and 2019.

“The FAA needs a confirmed administrator, and Phil Washington’s military and transportation experience made him an excellent candidate,” Buttigieg tweeted Saturday night. «The partisan attacks and obstruction of prosecution that he has faced are undeserved, but I respect his decision to retire and am grateful for his service.»

Washington ran transit agencies in Denver and Los Angeles, but his only aviation-related experience is serving as CEO of the Denver airport for less than two years. However, he has strong ties to the administration: He led Biden’s 2020 transition team for the Department of Transportation, which includes the FAA.

Biden nominated Washington last July but did not get a committee hearing for eight months. Republicans attacked her resume and seized on revelations that her name appeared on search warrants related to a corruption investigation in Los Angeles. Washington said that he did nothing wrong and that he had not been contacted by police.

The agency is led by an interim administrator, Billy Nolen, a pilot who has held security positions with three airlines and the FAA. Sen. Ted Cruz, R-Texas, who led the opposition to Washington, said Nolen could win bipartisan support.

In a statement late Saturday, Cruz said Washington’s lack of necessary experience was obvious.

“Given the significant challenges facing the FAA, this was not the time for an administrator who needed on-the-job training,” he said. “The Biden administration must now quickly appoint someone to head the FAA who has extensive aviation experience, can garner broad bipartisan support in the Senate, and will keep the flying public safe.”