David Gergen : Debate may represent Romney 's last big chance to turn around the race . Comment: Obama needs a big victory to claim broad support for his plans for second term , Gergen says .
David Gergen : Debate may represent Romney 's last big chance to turn around the race . He says the stakes are also sky-high for Obama , even if he wins election . Obama needs a big victory to claim broad support for his plans for second term , Gergen says .