A political group aligned with Senate Majority Leader Mitch McConnell plans a $27.3 million summer advertising blitz to help Republicans preserve the party’s Senate majority.

One Nation, a political nonprofit organization, is rolling out television and radio ads across six states where Republican incumbents are under fire. The biggest expenditure ($10.2 million) is planned for North Carolina, where Republican insiders are increasingly worried about the fate of Sen. Thom Tillis.