Erroll Southers, President Obama's nominee to head the Transportation Security Administration, withdrew his name from consideration Wednesday after months of delay in the Senate.

Southers — a former FBI agent and the assistant chief of homeland security and intelligence with the Los Angeles World Airports police department — was nominated in September and praised as well-qualified by many members of Congress. But his nomination languished for months after Sen. Jim DeMint, R-S.C., placed a hold on it. DeMint said he was concerned Southers would allow TSA employees to form a union.

The White House and Senate aides confirmed Southers' withdrawal Wednesday morning. A statement released by the White House blamed "political ideology" for stalling Southers' nomination. A White House spokesman said Southers would have made an "excellent" TSA administrator.

Union leaders — who supported Southers, in part because of his pro-unionization stance — said they were disappointed to see his nomination stall.

"I am disappointed with the withdrawal of Erroll Southers," said Colleen Kelley, president of the National Treasury Employees Union. "It was clear from the beginning that Southers was extremely well-qualified for this critical homeland security post. Two Senate committees agreed."

John Gage, president of the American Federation of Government Employees, urged the administration to quickly nominate a new TSA administrator. But Gage also said Obama could allow TSA employees to unionize before an administrator is confirmed.

And he swatted away criticism — from DeMint and several other Republican legislators — that allowing TSA employees to unionize would hurt national security.

"The burden's on them. It's not on us to justify why employees can exercise their constitutional rights to be a member of a union," Gage said. "Those who somehow just assume that being a union member compromises national security, they're the ones who need to put up or shut up. The explanations they've given so far are just fantasies."

DeMint's office did not respond to a request for comment.