The Rats need 15 seats to take control of Congress. Considering the fact that the out-of-power party typically makes the largest inroads during the off-year of a second term president, this is not out of the realm of possibility.
Hasn't happened since the "Republican takeover" of 1994, and the country has become even more conservative since then.
The GOP may not be a dream-come-true, but the Donkeys are even more pathetic.
With so many house districts gerrymandered in favor of one party or the other, less than 10% of house races will even be competitive. Things would have to break perfectly for the Dems for all these few races to go their way. If they actually had a program to govern on, I'd be more worried about that happening. In the absence of such a program, the most they can hope for is a pickup of a few seats, much less than 15.