Republicans entered the election with 54 seats, led by Kentucky's Mitch McConnell, versus the Democrats' 44 seats and two independent seats. Key Senate races:Arizona - Republican Senator John McCain, 80, faces an unexpectedly strong challenge from Democratic U.S. Representative Ann Kirkpatrick, 66. Indiana - Democrat Evan Bayh, 60, is trying to recapture his Senate seat, facing Republican Representative Todd Young, 44. Bayh or Young will replace Republican Senator Dan Coats, who is retiring. Illinois - Republican Senator Mark Kirk is trying to fend off a challenge from Democratic Representative Tammy Duckworth.