If the republicans maintain control of both houses its very possible that a third war, one with Iran, will begin, and have catastophic consequences for the world economy.
If the republicans maintain control it means the Military Commissions Act will begin to be implemented vigorously against citizens as well as non-citizens. Secret arrests, secret evidence, secret detentions, secret trials, all without even a requirement for charges, and indefinite sentences. American civilians will be tried by military courts martial. There is no check, or balance, or mechanism in place to prevent them from doing that, they have a clear road if they want to use it.
If the republicans maintain control it means out-of-control government growth, and continued disasterous deficits.
If republicans maintain control it means the full implementation of the security/survaillance nanny state. Already the Dept. of Homeland Security is preparing a requirement that Americans get government permission not just to leave the country, but also get permission to re-enter.
If republicans maintain control it means their continued betrayal of the sacred oaths they swore upon entering federal service to "preserve, protect, and defend" the Constitution, and Bill of Rights.