Elections serve as the most fundamental form of political accountability, and midterm elections provide an opportunity for citizens to participate in a single moment of collective accountability for the US president. Yet midterm elections serve not only as a judgement on the past performance of the president and his party; they also provide an opportunity to put in place a sub-federal accountability regime that oversees the president’s actions, a regime comprised of governors, state attorneys general, and mayors. It is this regime, reaching from city halls to the US Capitol building – and not simply the congressional midterm elections with which we are more familiar – that carries with it a ‘midterm mandate’ to redirect the president’s agenda. By reinterpreting, refusing to implement, or directly challenging federal policy, these actors complement Congress’s oversight function of the president.

Using the 2018 elections as a focus, this chapter surveys the growing importance of midterm elections as an opportunity to elect a cohort of actors who supply new sources of executive oversight. In surveying existing literature on governors, state attorneys general, and mayors, it argues that these are political actors of increasing salience on the national political scene as sources of accountability, and documents recent changes in midterm campaign strategy and donations that reflect this growth. Ultimately, the mandates carried and defended by this regime of subnational actors are transforming the significance of midterms on the national level.

According to conventional wisdom, midterm elections serve as a referendum on, or reassessment of, the existing administration and Congress. The 2018 midterms were no exception: Gary Jacobson labelled them an ‘extreme referendum’, ‘the most sweeping and discordant national referendum … since the Great Depression’. They reassessed not only the president, Donald Trump, and the Republican Party, but also Congress as an institution. Although midterms can serve as an assessment of the policy record of the preceding two years, they can also lead to horizontal accountability – that is, accountability between branches and levels of government. Midterms shape not only the partisan composition of Congress, but also subnational political institutions, and this, too, can provide a significant challenge to presidential authority. Winners in these elections complement the oversight activity in Congress. The 2018 midterms were also a commentary on the oversight role that the Republican-controlled 115th Congress played – or failed to play – in keeping the executive branch in check.