The case for divided government. Inclement political weather rocked President Obama and his party this summer. Falling poll numbers and growing voter misgivings open the door for big Republican gains in next year’s midterm elections.

But more storm clouds gather. With Democrats controlling the White House and Congress, the GOP can now use voter distrust of unified party control (the same party in charge of the presidency and Congress) as a tool to make major gains in next year’s elections–a political weapon both parties could only unsheathe irregularly over the past half century.