And I'll tell you why: The Republican party is currently having a quiet civil war within their own ranks between the reasonable old-school "country club" Republicans and the batshit insane teabagger crowd who are hellbent on destroying Obama even if it means destroying the country in the process. Currently, the lunatics appear to be winning and many of those up for election tomorrow are from the lunatic fringe.
If they win (and they might because much of the public is pissed at the Democrats in Congress for not getting the public option done already), then the Republican party will interpret that as a signal to run further to the right. They'll interpret an electorate that is either apathetic or pissed at Dems for not being liberal enough, interpret that as a reason to get more conservative and go full steam toward the right fringe. That's exactly what they did after the Gingrich landslide which worked for a while but led directly to W and the bloodbaths of 2006 and 2008 and it may work for them for a little while here as well but the further they run to the right fringe, the further away they get from the centre where political battles are won and the more their radicalism frightens people. Importantly, as well, the US is not the same as it was during Gingrich's time. A whole new population has come of age and they're mostly social liberals, the minority population is much larger and much more politically active and the most recent Republican admin before Gingrich was Reagan/Bush and as bad as they were in many ways, they weren't anything like the visible public calamity of W.
So, that's what I think will happen. They'll interpret any victory in the wrong way, run harder to the extreme right, scare the piss out of everyone reasonable and all the minorities, get absolutely whooped in 2012 (we're talking Reagan-Mondale whooped) and the party will be pretty much done for at least a generation (if it doesn't split).