U.S. diplomats breathed a sigh of relief three months ago when Rex Tillerson was nominated as secretary of state, welcoming the oilman as a seasoned manager who would shield them from ideologues ready to gut America's foreign policy machinery.

Yet that comfort is now giving way to unease, as the former Exxon Mobil Corp. chief embraces President Donald Trump's vision.

Tillerson supports the president's goal to cut the State Department budget and shift its mission away from existing initiatives such as climate change, global health and development assistance beyond key allies, according to half a dozen people familiar with his thinking who requested anonymity to discuss internal matters.