Donald Trump

Trump has threatened trade retaliation. And his presidency could herald new instability in the region if he pulls back on the U.S. security umbrella that's been in place since the end of World War II.

As Trump succeeds Obama, it is hard to imagine a wider gulf between sets of policies, or men with less use for each other. But such contrasts between consecutive administrations are the national norm.

The president-elect has said he will ask lawmakers to repeal the Affordable Care Act. Or he can use regulations and the budget to dismantle the federal health law he calls "a disaster."