ETA: @ SouthernYankee, it depends on what the core issue is. For example, although I am very liberal and almost always vote Democrat, I am pro-life. Most candidates who I vote for would publicly support a woman's right to choose. To me, social justice about a lot more than that one issue, so I don't let it get in the way. I'd rather vote for someone who believes in keeping abortion safe and legal but also thinks we have a responsibility to the poor and the middle class, the environment, accessible healthcare, marriage equality, religious tolerance, a compassionate and practical stance on immigration, etc. than for someone who claims to be pro-life but supports the gun lobby, Big Oil, corporate funding of campaigns, homophobia, disrespects women, etc. In my state, Party B candidates are pretty much middle-of-the-road types (otherwise they don't stand a chance of being elected) so it's not a huge issue here, but it's disappointing to see something like the pro-life movement, and the Catholic church (which I belong to) sometimes endorsing voting for extreme candidates or policies in other states just because of their stance on abortion or birth control or gay marriage without accounting for the fact that just about everything else the candidate espouses goes against church teachings.
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Honestly, it depends. I live in a mostly one-party state (et's call it Party A) and luckily, identify pretty closely with that party on core issues that are important to me.
For thing like the president, governor, senator and representative positions, I do my research and know why I am voting for whom.
With some of the lower-level positions, if I haven't heard about either of the candidates, I'll usually vote for the incumbent or Party A, which in my state, is usually the same thing. If there are major issues with the job that the incumbent has done, there has usually been enough press that I'm aware of the issues and will research before voting.
Many of our local positions are unopposed and/or party doesn't matter. If something local is contested, I usually know the people personally or have read and seen enough to make an informed choice.