It would be philosophical differences that define the members of the high court. Politics should not be part of the selection process. Clarence Thomas is a good example — the Democrats in the Senate did their best to block his appointment by playing dirty politics, just as the GOP controlled senate did to block Obama’s appointment who by all accounts is not a liberal. To answer your last question I seriously doubt that the GOP senators expected Trump to win — they wanted to deny Obama the opportunity to name another justice. I suggested that Obama should nominate Orrin Hatch to replace Scalia — what position would the GOP senators take?