House Republicans are reserving more than $18 million in ad time as they look to protect their majority.

The ad reservation, from the independent expenditure arm of the National Republican Congressional Committee, could potentially include 26 congressional districts and includes a mix of seats currently held by Democrats and seats where Republican incumbents are facing strong challenges. The initial reservation includes more than $3 million in ad time in California, about $2.2 million in the Boston area, more than $1.6 million in Colorado and about $1.3 million in Wisconsin.

As with House Democrats, who announced $32 million in ad reservations earlier this year, the NRCC could shift its spending or increase it. But the ad reservations offer an early idea of where Republicans think they will play offense and defense.