David and Helen talk to Shashank Joshi, Defence Editor at the Economist, about the fallout from the killing of Soleimani and the future of American power. Is Trump a madman or is he a realist (or is he neither)? What sort of threat does Iran pose to American interests in the region and the wider world? And what has all this got to do with oil and climate change? Plus, in the week Trump's impeachment trial gets underway, we ask who or what can limit the power of the presidency.