That’s according to three people familiar with his decision. They spoke on condition of anonymity to discuss deliberations before a formal announcement.

Nielsen was former DHS Secretary John Kelly‘s deputy when he served in that role and moved with Kelly to the White House when he was tapped to be Trump’s chief of staff.

Elaine Duke has been filling in as acting secretary in the meantime.

Neither the White House nor Nielsen responded to requests for comment.

Neilsen is an expert in homeland and national security policy. She previously worked as a special assistant to George W. Bush and for the Transportation Security Administration.

The plans were first reported by Politico.