Angela Merkel is on her last lap as German Chancellor and will stand down when September’s federal election ends her fourth and final term in office. Meanwhile her party, the ruling Christian Democratic Union, is trapped in a high-stakes stand-off with its Bavarian ally, the Christian Social Union. The impasse? Which of their leaders should guide their centre-right alliance through the upcoming election campaign, the first in over two decades without Mrs Merkel at the helm. In this episode, the Irish Times Berlin correspondent Derek Scally has the latest in Germany's unfolding political drama.