Updated

The experiences Ashton Carter would bring to the job of defense secretary are vastly different from Chuck Hagel's in several important ways — starting with the fact that Carter is an academic and a policy wonk.

How Carter would pursue President Barack Obama's defense agenda, or use his influence to bend it in new directions, is less obvious.

Unlike Hagel and every other man who has led the Pentagon over the past 30-plus years, Carter has served neither in the military nor in Congress. Hagel did both. And although he moved in national security circles for years, including his time as head of the Atlantic Council, Hagel was never seen as a master of policy.

Obama plans to announce Carter as his nominee on Friday.