Why do party activists impose so-called litmus test on potential supreme court nominees

The party activists impose a so-called litmus test on potential Supreme Court nominees to determine whether they are politically inclined towards the party's ideology or not.

Explanation:

The litmus test in politics is simply to determine whether the candidate supported by the party complies with the party's ideology or not. It is to make sure that once the candidate is appointed to the post of authority, would he or would he not prove beneficial for the fulfillment of the issues on the party's agenda.