WASHINGTON – Hoping to make the third nomination the charm, the White House announced Monday that President Obama would nominate FBI Deputy Director John Pistole to head the Transportation Security Administration.

In a statement, Obama said Pistole’s work with the FBI makes him a valuable asset to the administration’s efforts to strengthen security and screening measures at airports.

Obama has struggled to fill the top job at TSA, the agency whose primary mission is to shore up the nation’s defenses against terrorist threats. The Obama administration has called the job the most important unfilled position on the president’s team.

Obama’s first choice for the post, Erroll Southers, withdrew his nomination after it became apparent he would have trouble winning confirmation. Questions were raised about a reprimand that Southers, a top official with the Los Angeles Airport Police Department, had received for running background checks on his then-estranged wife’s boyfriend two decades ago.

Obama then nominated Retired Army Maj. Gen. Robert Harding, but he took himself out of the running in March.