Contrary to the views of most politicians and scholars, the current situation, with an eight person Court equally divided among Democrats and Republicans (and conservatives and liberals) is actually a very good thing. In fact, there are compelling arguments that maybe we should stay with an equally divided 4-4 Court for as long as possible.
. . .
First, with eight Justices equally divided between the two major political parties, the winning side must convince at least one Justice to side with Justices from the other party to form a majority. Over time, this requirement would lead to more public confidence in the final outcomes and also likely generate more moderate arguments and decisions (which is a good thing given that the Court is composed of life tenured, elite lawyers who the people dont elect and cannot vote out of office).
Second, with eight Justices divided along political party lines, it will be much harder, though certainly not impossible, for the Court to overturn decisions by more accountable governmental officials. The Court could still play an important role as many of its historic decisions would not have been affected by an even number of Justices. For example, Brown v. Board of Education was 9-0, Roe v. Wade was 7-2, and Reynolds v. Simms (one person-one vote) was 8-1. But with only eight Justices, there will be none of those obviously partisan 5-4 decisions that sharply divide the country such as Citizens United (campaign finance), District of Columbia v. Heller (guns), and Shelby County v. Holder (voting rights). That is not to say that there wont be divisive 5-3 decisions or even 8-0 decisions but at least in those cases the votes cant be purely along party lines.
Third, constitutional law is tricky business to say the least. Most constitutional disputes involve ancient and vague text, contested historical accounts concerning that text, and fuzzy precedent. One does not have to be a hard core legal realist to believe that personal values, politics, and ideology play a prominent role in Supreme Court cases. Having an equally divided Court over time would likely reduce the infection of politics and personal values in the Justices decisions because to accomplish their goals, the Justices would simply have to get along better.