'Perfect Storm' Could Pin Senate Majority on Late Washington State Returns

In seven of those races, the Republican candidates hold modest-to-comfortable-to-double-digit leads. The three uber-toss ups are Nevada, Illinois and Washington. Not only is Washington the last of those to close, with polls shuttering at 11 p.m. ET, the state's voting rules and reputation make for a predictably slow count. 

"The perfect storm would be Republicans pick up nine seats and everyone's waiting to see what happens in Washington for days," said Todd Donovan, political science professor at Western Washington University.