The criticisms of the appointment and confirmation process of the Supreme Court are centred around the evidence for the almost certain probability of politicisation by the press, Senate and the President. The main point of politicization occurs through the the President though, as it is he who nominates the Justices.
Although a President would never admit to appointing a Justice based on their political ideology, this is normally the case in reality. Appointing a Supreme Court Justice is not something every President is gifted with and as such they tend to use it to their advantage, both whilst they are in office and after. What is meant by this is that, for example, a President who is conservative will seek to appoint a Justice whose views are also known to be conservative. This is mainly for two reasons; he will want to have as much support for his bills as possible and because they can provide a sort of legacy for the President after he has left office. The way in which a Supreme Court Justice can support the President is that they will be more likely to agree with policies coming from a President with a similar ideology to them. Furthermore, the Supreme Court has famously been described as an "echo chamber" for past Presidents due to the fact that any judge appointed by a President will almost certainly be there long after the President. A great example of this is by President G. W. Bush. President Bush nominated Roberts after Justice Sandra Jay O'Connor announced retirement in 2005, however, surprisingly Chief Justice Rehnquist died. Due to this, Bush then withdrew Roberts from an ordinary Justice nomination, and instead put him forward as Rehnquist's replacement. This highlights Presidential politicization within the Supreme Court as Bush clearly wanted to gain a significant political foothold in the Supreme Court by appointing a young Judge with the same ideology. As well as this, Presidents often use a "litmus test" as a decider.