This article describes a social experiment facilitated by CBS This Morning co-host Tony Dokoupil, where he showed Republicans and Democrats the exact same clip of a confrontation between police and protestors. He asked each person who was the aggressor in the situation. Democrats were overwhelmingly more likely to say the police, while Republicans were overwhelmingly more likely to say the protestors. 

The article also references the concept of the "bias blind spot," meaning that individuals often have trouble determining when they are being biased.