Midterm-Election Ad Spending Poised to Soar as Streaming TV Attracts Campaigns

A top advertising-industry observer expects elections this year and next will see political ad expenditures of roughly $9 billion, more than doubling the amount spent in the 2018 midterm cycle.

The spots are also likely to increasingly appear on television screens connected to the Internet by streaming-video players such as those made by Roku Inc., which dominates the device portion of a rapidly growing market known as connected TV.

AdImpact, a firm based just outside Washington, says in a report first shared with The Wall Street Journal that it expects ad spending to...