Key points:

- The Democratic Party is narrowly favoured to retake the House of Representatives in November’s midterm elections, but Republicans are expected to retain the Senate majority.

- Should Democrats win control of the House, the Trump administration will struggle to deliver on its legislative agenda prior to the 2020 presidential election.

- The midterms will shape the ideological orientation of the Republican Party, which is being remade in President Trump’s image, and the Democratic Party, which is moving further to the left.

- Deepening polarisation between the two major parties will limit the US government’s ability to reach bipartisan compromises on foreign and defence policy, pass the federal budget on time, and avoid government shutdowns.

- After the midterms, Congress is highly unlikely to support – let alone vote in favour of – US re-entry to the Trans-Pacific Partnership.