Turnout in North Carolina was 44%, an historically high number for a mid-term election in the years since instant registration. Democrats cannot blame the outcome on bad turnout. It's true that in 2008 when Kay Hagan was elected to the U.S. Senate, statewide turnout was 75% — but that was an exceptional election, driven by the presidential race. If Democrats require 75% turnout to win statewide elections in North Carolina, they are toast.
Given the turnout, it's difficult to argue that voting was significantly suppressed by changes to the voting process implemented by Republicans.
Democrats do need to figure out how to get young adults back into the voting booths. In the comparison between 44% and 75%, the biggest delta was the turnout of young adults. Pollsters didn't see this coming (see below).
Although most county-wide elections in Wake County were won by Democrats in the 54-56% range, Republicans lost only one seat in the Wake County delegation at the North Carolina General Assembly. Why? Because of how the districts were drawn after the 2010 census. The consequences of the 2010 election, a disaster for Democrats, will remain with us until at least 2022 when the next redistricting will take effect.
The gerrymandering of 2010 — nothing new in North Carolina politics, remember — does not nullify the fact that the election showed no evidence of widespread dissatisfaction with the actions of the General Assembly. In mid-term elections the party not in power in Raleigh typically gains ten or more seats in the General Assembly. Not this time.
Democrats expended the same amount of money on campaign advertising as Republicans. These races were not bought by rich Republicans.
Curiously, the Democrats won statewide judicial elections in North Carolina. No one can explain why.
60% of unaffiliated voters in North Carolina voted Republican. "It's the economy, stupid." If you look at the counties where Hagan captured a much lower percentage of votes than in 2008, you find counties where unemployment remains stubbornly high. The economy is much-improved in the Triangle, which voted Democratic, but that's not the case throughout the state. As George H. W. Bush learned in 1992, voters are quick to take out their frustrations about the economy on incumbents. It might not be fair, but it's real.
President Obama's approval index has been in negative territory for 18 months. Among Democrats, few state or local candidates wanted to associate themselves with the unpopular Obama. Arguments about whether Obama's approval index should or should not be negative are pointless. It is negative. Republicans successfully turned the 2014 election into a national referendum on Obama. Hillary Clinton had better explain to voters how her administration would be different from Obama's.
At the national level, there was ineffective cooperation (if not outright conflict) between the White House and national Democratic Party operatives. Regardless of whom one blames for it, a house divided...
Credibility of pollsters took a big hit because most of them failed to predict such a strong Republican victory nation-wide. Pollsters do make adjustments to their statistical models after errors such as this, but those adjustments are necessary retrospective and not necessarily accurate in the next election.