Rove & Company have narrowed the battlefield (or at least that's what they're saying for public consumption):

They have determined that control of Congress is likely to be settled in as few as six states and have decided to focus most of the party’s resources there, said Republican officials who did not want to be identified discussing internal deliberations. Those states will likely include Connecticut, Indiana, Missouri, Ohio, Pennsylvania and Washington, though officials said the battle lines could shift in coming weeks.