In over twenty years, there have only been two times that I have voted for general election candidate I agreed with 100% of the time. Both of those times (in 2006 and 2015) I voted for myself. Every other time, I have voted for candidates that I have disagreed with, if only on small matters.
The real question is how much disagreement one can tolerate while making the best choice of all available options. Everyone has a point where they will not support the a candidate of their chosen party. (At least I hope they do!) The question is where to draw that line, and that line differs from person to person.
People may not support their party’s candidate for any of a number of issues: Private property rights, gun control, abortion, tax policy and many others. Some people are single-issue voters where others take a more comprehensive view of a candidate. Even when voters of particular party agree with a candidate on most issues, they might find that candidate lacking in moral character and refuse to vote for him for that reason.
But apart from those exceptions, we all compromise every time we step into the voting booth. There are many reasons why we make those compromises, or the reasoning might be very narrow.
For example, party affiliation matters a great deal in state legislative bodies and in Congress. This is why someone may not vote for a candidate that is closest to his own views (such as a conservative who votes for a moderate Republican over a conservative Democrat) because he realizes that if the Republican Party controls the speaker’s chair and committee chairmanships the end product will be better even if his own legislator votes the “wrong” way.
We all make those decisions according to our own consciences and what we think is best.