As the United States gears up for midterm elections Nov. 3, voters are weighing not just the balance of power in Congress, but also a host of issues in state ballot measures. In 39 states, the public will decide 145 such measures, in which people vote directly on changes to state laws or constitutions.

Ballot measures often reflect local issues in each state, says John Matsusaka, executive director of the Initiative and Referendum Institute at the University of Southern California. But sometimes, “there are issues ... that happen at the national level that spark a response across multiple states.”

That dynamic is playing out this year, with many ballot measures reflecting policies that have taken center stage during President Donald Trump’s second term. More than 15 states are mulling changes to how they conduct elections, including some that might revise their redistricting rules or congressional maps.…