President Trump told reporters on Air Force One that he now has five finalists for the position of national security adviser, though an aide later said there were more.

Trump named attorney and U.S. hostage negotiator Robert O’Brien, assistant to the chairman of the Joint Chiefs of Staff Ricky Waddell, Energy Department nuclear security expert Lisa Gordon-Hagerty, former National Security Council chief of staff Fred Fleitz, and retired Lt. Gen. Keith Kellogg, who currently advises Vice President Mike Pence.

Trump seemed to implicitly rule out leading contenders with large bases of support, including retired Army Col. Douglas Macgregor, a favorite of noninterventionists, U.S. Ambassador to Germany Richard Grenell, and U.S. special representative for Iran Brian Hook.

Trump's comments reflect his current thinking, but he has been known to change his mind frequently during the process of considering staff hires.

O'Brien, who has a strong personal rapport with Trump, appears to have emerged as a front-runner recently, according to two sources close to the White House. Many insiders are unfamiliar with his policy leanings, however, and some suspect that Trump would not want to gamble after coming to regret the selection of early administration figures.

Waddell, widely viewed as low-key and even-keeled, is close to Secretary of State Mike Pompeo, who is expected to play a leading role in the selection after reports that he was personally interested in filling the role — an option that Trump downplayed last week.

Gordon-Hagerty was not widely discussed as an option before Trump named her. She also leads the National Nuclear Security Administration.

Fleitz formerly worked as chief of staff to fired national security adviser John Bolton but has maintained close links to the White House. He previously was under consideration to become director of national intelligence, though there were questions about whether the Senate would confirm him.

Kellogg, meanwhile, is seen as a potential hands-off national security adviser — a job that comes with a prime corner office in the West Wing overlooking the White House driveway.

"The president really likes him personally, [but Kellogg] is just not an in-the-weeds kind of guy," said a former senior administration official. "He's been retired for a lot of time. He likes being at the White House. He likes being on the plane. He likes giving the president his opinion. He doesn't like nitty-gritty policy minutiae."

White House Press Secretary Stephanie Grisham Tuesday evening said there were more than five names on Trump's list.