Angela Merkel Starts Fourth Term Facing Big Hurdles

BERLIN—Angela Merkel finally began her fourth and likely last term as chancellor on Wednesday, a step that presents her with some of the toughest domestic and international challenges in her years in power.

Germany’s parliament formally elected Ms. Merkel after the longest and most-complicated coalition-building exercise in post-war history. As she heads a fractious government of political opposites whose popular support is waning, Ms. Merkel will have to fend off economic threats from the U.S., address neighbors’ demands…