Can you prove bias

A headline the other day said that the ninth circuit court, the bastion of liberalism is threatened by new Trump appointees. When judges are deemed to be biased it only makes sense that those in congress would be biased. It then follows that those who work for these politicians would be biased. In spite of that investigators keep saying they could find no proof of bias. Those being investigated say they are biased but it does not effect their work. Senator McConnell is accused of bias toward Trump. Will the democratic senators running for president who will act as jury members in the impeachment be biased. They say they will not let their personal opinions cloud their judgment.