Few would have expected Angela Merkel to stand in, let alone survive, another election at the height of the refugee crisis in 2015. And yet, two years later, Merkel is set to remain Germany's Chancellor, with her party winning the most votes in Sunday's election.

The road ahead, however, will be rocky for the "eternal Chancellor" and Merkel's to-do list is full of tasks that would make the most skilled politician squirm…