President Donald Trump appointed retired Army Lt. Gen. Keith Kellogg as acting national security adviser after Michael Flynn's resignation.
Kellogg, 72, is one of several potential picks for the permanent post, based on what senior administration officials told NBC News.
Kellogg, a decorated Army veteran, was a top policy adviser for Trump during his campaign and among the original contenders before Flynn secured the job, according to NBC News.
Other possible picks: Former CIA Director David Petraeus, retired Vice Admiral Robert Harward and former National Security Adviser Stephen Hadley.
Petraeus, 64, is a retired four-star general and was once America's top official in the Iraq and Afghanistan wars. He had to step down as CIA director after it became known in 2012 that he shared classified information with a biographer who was also his mistress.
Harward, a former Navy SEAL, is the front-runner for the job, three senior officials told NBC News. Harward spent almost 40 years in the Navy and was on President George W. Bush's National Security Council with experience in several Middle Eastern countries as well as Somalia and Bosnia.