Brendan Nyhan checks to see and it turns out that, yes, the GOP is hugely unpopular in historical terms:
But what does it mean for the midterms:
In short, there’s no question that the GOP party brand is in worse shape than any opposition party in recent memory. The question, however, is whether this difference in party valence will (a) persist through next November and (b) translate into fewer GOP House seats at the polls, especially once we account for the generic Congressional ballot, which should (in principle) take much of this difference into account (see Alan Abramowitz’s model, for instance). Those questions remain to be addressed.
I would say the problem for Democrats is that the voters can’t coordinate their actions. A person who would like to see the congressional Democrats brought down a notch or two may vote Republicans even if he doesn’t really want to see John Boehner take over as Speaker—especially if he thinks a GOP takeover scenario is unlikely. But if a whole bunch of people do that, then the GOP does take over, whether or not that’s what people intended to have happen. Conversely, it’s possible that Democrats will be able to improve on their current generic ballot position by focusing voters’ attention on the possibility of a Republican takeover.