One could simply support a candidate for their choice of SCOTUS judges or recognition of Jerusalem as the capital of Israel or opposition to TPP. It's not necessary that a voter endorses everything that the candidate has ever done in their life. I find this standard to be largely driven by the media. The President has a governing role, and different people are affected by it differently. If he is a terribly rude and obnoxious jerk - sure that can be a part of one's judgment, but it's not necessary that everyone has the same hierarchy