Speaking at an event in Washington, William McRaven, a SEAL who oversaw the bin Laden raid, said the US was approaching a "Sputnik moment" with China.
"There's not a hesitation," Jim Mattis said. "I'm just trying to think how to say 'no' even stronger."
A new policy affecting the citizenship of children born to some US service members appears to have surprised the Department of Defense.
There's been more Chinese ship, fighter, and bomber activity in the contested waterway this past year than any previous year, a top US official said.