Today, Judge Kavanaugh made the argument in sworn testimony, and this argument was backed up by the Republicans in the room, that all the accusations against him are a Democratic conspiracy. He also made the assertion that this conspiracy has permanently and irreparably destroyed his life, his family, his relationship to his children, his career and his reputation. This places a huge dark cloud over the Democratic party in his mind.
The Supreme Court of the United States is often the place where US laws meet their final and ultimate challenge. The Supreme Court Justices have to listen carefully and in an unbiased fashion to arguments that a current law is constitutional, vs. not constitutional. The Supreme Court does other things, they look at other kinds of cases, but this is a very common and critically important mode of operation for SCOTUS.
The lawyers charged with arguing in favor of the standing US law are part of the executive branch. They are part of the President’s team.
If Kavanaugh becomes a justice of the Supreme Court, he will have to recuse himself in any case where a plaintiff argues against the constitutionality of a standing US federal law. He has demonstrated a powerful, permanent, and indelible bias.
He won’t make much of a judge if he can’t really do his job.