Yes, party affiliation is certainly part of the problem. Also, there seems to be a "s/he thinks like I do" effect. That's what Trump's and Putin's bases seem to think of them, for example, and maybe that's why most of us support the politicians that we do.

Some people, unfortunately, advocate violent behavior vicariously. A lot of people have said "I hope somebody kills Putin", and that disturbs me. He needs to be removed from power and imprisoned for war crimes. But to advocate assassination of one's enemies is to encourage dangerous (murderous) behavior by other people.