NBC News hasn't yet called the Senate race in Pennsylvania, where Republican Dave McCormick holds a narrow lead over Democratic Sen. Bob Casey.

Ticket-splitting used to be common and the swing-state down-ballot results show split tickets still can determine the outcome of key races.

Republicans are favored to win control of the House but it could be with a slimmer margin than they currently hold.

This could give Republicans sweeping powers to potentially ram through a broad agenda of tax and spending cuts, energy deregulation and border security controls