Defense Secretary James Mattis arrives at the Pentagon and will likely have to get right to work forging a plan to defeat ISIS and tackling budget and staffing issues.
Mattis, a retired four-star Marine Corps general, is expected to spend part of the first few months traveling to visit troops abroad and reassuring allies in Europe and Asia. But, experts say, there may be unexpected world events that could upset his plans.
"There are wildcards of unexpected world events that could intrude," said Mark Cancian, a senior adviser with the Center for Strategic and International Studies' International Security Program in Washington, D.C. "Those are very hard to predict."
Mattis will have a critical role in shaping and implementing President Donald Trump's plan to rebuild the U.S. military, including adding more troops, ships, and aircraft. The former general also may be asked to help sway members of Congress to undo the sequestration budget caps to allow for more defense spending.