Voters in the swing state Wisconsin will head to the polls on 4 April to determine who will replace Justice Patience Roggensack on the state supreme court. It is down to the final two – a liberal and a conservative – and the outcome will determine majority control of the court for at least the next two years, including during the presidential election in 2024. It is expected to be the most expensive election of its kind in history. Joan E Greve speaks to Alice Herman and Sam Levine about what is at stake