On the graph for popularity of the Republican Party: the "40" is roughly the same as it was in the spring of 2010 just before the Tea Party landslide in the House and in the spring and summer of 2014, just before the Republicans took a majority in the Senate and projected themselves to be the majority Party for the next couple decades. They have nearly enough power that if they win big in November 2016 they can marginalize the Democratic Party into near-irrelevance as an impotent opposition limited in authority to a few ultra-safe areas (New England, the West Coast, and giant cities). The lows are not getting significantly lower for the GOP, even if the highs for the GOP are going lower. For Democrats to win much of anything that they lost in 2010 or 2014 they must catch the Republicans in a low (really 40% or lower) in November. For good reason I do not predict political trends unless those have have a basis in demographic change. I got burned in predicting the 2006 and 2008 elections as evidence of American readiness for fundamental change in the political order.
I expect the Republicans to ramp up their usual fear-laden negative campaigns and to bring more political threats to the workplace -- basically that "if you don't want to be laid off, then vote straight Republican".
It's not the specific point it's at now that is important IMO, it's the trend it represents since 2010. Their approval ratings may go up at least somewhat after the nomination is settled, but even in 2014 their approval ratings remained decently lower than that peak in 2010. I think it's without doubt that their brand has sustained damage. To say they will recover back to that 2010 peak, or close to it, seems unlikely if they couldn't do it at any time between Jan 2011 - now.The point going into the election period determines what is possible. In 2010 right-wing interests heavily pushed the Tea Party revolt against the recent Democratic majorities in Congress and above all our 'exotic' President. Those right-wing interests wanted to intensify right-wing economic trends from when Ronald Reagan was President... and succeeded.
Democrats must win the total vote for the House by about 54-46 to win the House. They got the majority of nationwide votes for the US House in 2012 and still fell neatly short of a House majority due to gerrymandering of Congressional districts.
The "Establishment" wing of the Republican Party has been extremely unsuccessful in getting its potential nominees to the level of support necessary for nomination. But that wing still controls the Party apparatus. It has gotten its 'profits first, people never' agenda pushed in Congress with the aid of people more opposed to abortion, secularism, feminism, and homosexuality than intent on wage cuts and tax cuts, They were promised an abortion ban, school prayer, creationism, and suppression of 'gay rights' in return for their acquiescence with the Hard Right on economics. The Hard Right got the economic agenda but delivered nothing of the 'social' agenda. For that the Hard Right could still pay a high price in electoral politics.
Donald Trump is a lose-lose proposition for the Hard Right, at least this time. He does not project to win, and he isn't even close to being in position to defeat either Clinton or Sanders. His demagoguery makes him unreliable if President, but should the GOP Establishment swat him down in favor one of their own, then the GOP Establishment demonstrated the heavy hand of its politics. That will offend many moderate-conservative voters who could stay home, vote for a third-party or independent conservative candidate, or even vote for the Democrat this time.
I expect the Koch brothers to spend heavily on negative campaigns against any Democrat who can be defeated. Remember their ethos -- no human suffering is excessive if there is a profit to be derived from it. But these campaigns may become less effective each time. Republicans have a huge number of Senate seats to defend, and defending a large number of Senate incumbents will be costly and tricky.
A Democratic win of a Senate majority doesn't require much of a wave. A Democratic win of the House will indicate a wave. How unpopular must one get to lose a House seat? Think of all those young adults who have some combination of huge student loans and low wages. Such people have no stake in Movement Conservatism that would turn anyone not born into the elite into quasi-serfs.
Republicans have many ways to achieve electoral disaster. The biggest possible asset that Republicans had going into 2016 was tepid support by America for an incumbent President. Through their bad choices they have frittered that away.
