Ashton Carter, the former second-in-command at the Pentagon, appears to be the top choice to replace outgoing Secretary Chuck Hagel. 

Barring any last minute complications, Ash Carter will be President Barack Obama's choice as the new Secretary of Defense, several U.S. administration officials told CNN. 

An administration official had said that Homeland Security Secretary Jeh Johnson, a former General Counsel at the Pentagon, was also still on the list of possibilities, but on Tuesday morning, sources said Johnson was no longer being considered. The prospect of an additional confirmation hearing for Johnson's replacement if he were to move to the Pentagon as the Senate switches to Republican control would have been problematic for the White House. 

Related: Was Hagel doomed from the start? 

Hagel announced his resignation last week, but has said he will stay on until his successor is confirmed by the Senate. 

Carter, who served as Deputy Defense Secretary under both Leon Panetta and Hagel, would bring a wide range of experience to a department confronting multiple crises in the Middle East and preparing to enter a new phase in Afghanistan as the NATO combat mission ends. 

Carter's ability to hit the ground running from his past experience at the Pentagon, in addition to the respect many senior military leaders have for him are seen as major benefits to winning confirmation should Obama nominate him. 

"His career has sort of prepared him perfectly for this kind of a moment," says Michael O'Hanlon, a defense industry analyst at the Brookings Institution. 
how long will he stay?
until his successor is confirmed