A large block of voters is really ticked off with Republicans. These are those voters who voted for Republican candidates who promised one thing and then when elected failed to vote the way they said, while running, they would vote.
Yet there are those in the GOP leadership who say, quietly or openly, that "well, voting to re-elect such Republicans is better than voting for a Democrat…" But what those leaders don't realize is that to many would be Republican voters that's not true. They will simply not vote, donate to, or work for, if they are not offered a choice they feel good about.
It should be noted that we're not talking about even a majority of those who would vote Republican. What the exact percentage is cannot be determined until after an election, but of this you can be sure: It is a large enough percentage to affect the outcome. Mitt Romney found out that it was nearly four million. Had a good portion of those people actually voted, in the right states, Romney would have won the electoral vote.
Here's Why Republicans Hate The Republican Party http://thefederalist.com/2015/07/27/heres-why-republicans-hate-the-republican-party/