What’s at stake in the US midterm elections?

November's midterm elections in the US are the first chance for voters across the country to pass judgement on President Trump's administration since the 2016 election. All 435 seats in the House of Representatives are up for grabs and a third of the Senate. If the Democrats win control of the House, they would not only be in a position to halt President's Trump's legislative agenda; they would also be able, should they wish, to start impeachment proceedings. On The Briefing Room this week David Aaronovitch asks what's at stake in these elections and how the outcome will reshape the American political landscape two years before the next Presidential election in 2020.