“Mattis is the canary in the coal mine”

In Asia, Mr. Mattis, a retired Marine four-star general who spent years leading troops in Iraq and Afghanistan, will confront steadily deteriorating security conditions on the Korean Peninsula, in the South China Sea and across the Taiwan Strait. All are complicated by fraying ties among traditional U.S. allies in the region and confusion over the new administration’s approaches.

But his trip is commanding attention beyond the region. Later this month, the U.S. defense chief is expected at a pair of security meetings in Europe, where allies see him as someone who can act as a buffer between some of President Donald Trump’s more impetuous moves and U.S. interests abroad. If Mr. Mattis were to leave the job or lose influence within the administration, it would be seen as a troubling omen, said one foreign official.

“Mattis is the canary in the coal mine,” the official said.