As Germans head to the polls on Sunday to vote in pivotal legislative elections, immigration will be a key issue on their minds. It's nearly 10 years since Angela Merkel's famous phrase "Wir schaffen das" (We can manage this), when images of German citizens welcoming asylum seekers made headlines the world over. Since then, the tide has turned and the far-right AfD party has become Germany's second political force. Our correspondents report.