Are Senate Republicans facing an election wipeout?

It's still a ways off, but Democrats are feeling very good about their chances of winning control of the U.S. Senate. Right now, they are four short of being the majority party. (That is, if Democratic nominee Hillary Clinton wins the presidency and Tim Kaine, as vice president, therefore becomes president of the Senate and can break a tie vote.)...
http://thehill.com/blogs/pundits-blog/campaign/294240-are-senate-republicans-facing-an-election-wipeout