The answer is this guys...
You'll know if a person is truly politically objective if that person is able to accurately describe his opponent's beliefs.
That's the ultimate sign.
Partisans can't do this, they always lie and/or exaggerate the other guy's beliefs and/or arguments.
If a person is unwilling and/or unable, don't know which one is worse, to accurately describe what their political opponent believes then that person is just a partisan and can never be objective.
Someone said if they can criticize their own side, which is kind of close, but the ultimate sign if hey can describe the other guy's position fairly.