Julian Zelizer : Midterm elections could change the balance of power in Congress . Zelizer : If Democrats win , they can force compromise ; if GOP wins , it can torpedo Obama . Comment: Zelizer : Elections will also offer a huge stage for possible presidential candidates .
Julian Zelizer : Midterm elections could change the balance of power in Congress . Zelizer : If Democrats win , they can force compromise ; if GOP wins , it can torpedo Obama . He says midterms will be a glimpse at challenges and promises parties will offer in 2016 . Zelizer : Elections will also offer a huge stage for possible presidential candidates .