President Donald Trump on Wednesday said he will nominate Kirstjen Nielsen to be secretary of Homeland Security, promoting a chief aide of John Kelly, his chief of staff and former Department of Homeland Security head.

Nielsen served as Kelly’s chief of staff at DHS until he was tapped by Trump to be his chief of staff in July. She has been Kelly’s deputy at the White House since then.

Prior to joining Kelly at DHS, Nielsen spent seven years at George Washington Univ.’s Center for Cyber and Homeland Security, a think tank doing public policy research and analysis, according to her LinkedIn profile.

In the past few years, Nielsen has also advised NATO and the World Economic Forum, and worked at her own consulting firm.

During the administration of President George W. Bush, Nielsen was a senior legislative policy director at the DHS Transportation Security Administration. Also under Bush, she was a special assistant to the president and senior director for Prevention, Preparedness, and Response on the White House Homeland Security Council.

If confirmed, Nielsen will be the second woman to lead DHS. The first was Janet Napolitano, who was President Barack Obama’s first DHS chief. The department is currently being led by Elaine Duke, who is the deputy secretary but is in charge of DHS in an acting capacity.