Is it common for a supreme court selection to have strong ties to a
political party? I don't remember anyone like this being a pick for
the supreme court during my lifetime.
And are there any written/legal or unwritten reasons or historical
precedent on why a person with a political past should not be voted
onto the Supreme Court?
Strong political connections and support are pretty much pre-requisite to any appointment to the federal judiciary. At least 95% of federal judges have strong political ties. This is a long standing reality dating back to before the 1800s.
This is a natural and expected consequence of the fact that federal judges are appointed by elected officials and confirmed by elected officials.
Arguably, it is a feature and not a bug.
While courts in many countries rule only on questions of private law (i.e. disputed between private citizens) and criminal law (in which the state intervenes in a dispute between private citizens), U.S. courts, and especially the federal courts in the U.S., have always had broad public law (i.e. disputes between the government and individuals or other governments) jurisdiction. Again, this is something that dates, at least, to the early 1800s.
Judges with political connections and supporters are more capable of fully understanding what is at stake in public law disputes and handling them adroitly.
Judges still need to be able to rule impartially in accordance with principles of law, rather than purely out of personal partisan beliefs, so the political aspects of a judge's judicial philosophy and a capacity to be impartial still matters. But, merely being politically connected is a job requirement, not a disqualification.
This doesn't mean that Democrats and moderate Republicans aren't justified in opposing him because his history clearly demonstrates that his views are out of the mainstream and that he may have great difficulty being impartial. But, it is what his past says about the kind of person and kind of judge he is that matters, not the mere fact that he has political connections.