When explaining the design problems with the Supreme Court, people often point to the fact that the judges are unelected or the fact that they are appointed for life. While it is fair enough to dislike these design choices, it does not seem to me that either of them are fundamentally problematic in the sense that they frustrate democratic control. The thing that frustrates democratic control is strategic retirement, which allows sitting judges to effectively select the political leanings of their successors into perpetuity.
Supreme Court judges are themselves unelected, but they are appointed by the President and the Senate, which are elected. This is how most of the important parts of the government are staffed, including the Secretary of the Treasury, the Secretary of Health and Human Services, the Secretary of Defense, and so on. Unless you think appointments are inherently illegitimate, even when done by democratically-elected representatives, the fact that the Supreme Court is unelected should not be seen as a fundamental problem.
Lifetime appointments are certainly weird in that they create variable judicial term lengths that are unknowable in advance. They also create long term lengths, 16 years on average. This is compared to 2 years for the House, 4 years for the President, and 6 years for the Senate. But judges do eventually die, meaning that the ideological composition of the court is theoretically able to be changed along with the results of Senate and Presidential elections, just as the ideological composition of other appointed positions are able to be changed in this way.
The core design flaw that enables the SCOTUS to turn itself into a self-sealed power structure is that judges are allowed to retire and thus allowed to choose when to retire. In almost all cases these days, judges choose to retire when the political conditions ensure that they are replaced by someone with their same ideology. These strategic retirements allow the court’s ideological composition to go unchanged potentially into perpetuity, totally insulated from average changes in the results of Senate and Presidential elections.
When all judges partake in strategic retirements, the only thing that can realistically cause the court’s ideological composition to change is surprise deaths that happen to occur when the political conditions result in the appointment of an opposite-ideology successor. This is rare and also not skewed in the direction of one ideology or the other, meaning that it’s likely a wash overall.
Absent surprise deaths, the only way to change the ideological composition of the court in the face of strategic retirements is to control the Presidency and the Senate for many consecutive decades so that some judges die before they have a chance to strategically retire. It is extremely rare for any party in any democratic country to have control of the government for that many consecutive years and the number of years required for this strategy is growing as judges get appointed at younger ages and life expectancy rises.
The most obvious way to narrowly fix this design flaw would be to take the idea of a “lifetime term” more literally. When a new judge is appointed, the term of that judgeship should be for as long as that judge is living. If the judge retires, then they can be replaced, but the replacement is only able to serve out the rest of the term, which ends when the retired judge dies. This is, after all, how mid-term retirements for the President, House, and Senate work: replacements are selected but only to serve out the remainder of the term.
What we have now is not really a “lifetime term” but a “lifetime or retirement term.” And the retirement part of that can be and is used to create a Supreme Court whose ideological composition is effectively permanent and outside of the control of democratic bodies. When you combine this feature of the court with the court’s self-appointed power to declare laws unconstitutional, you have a truly rogue element of the governing system that is intolerable and almost certainly not anticipated by the people who came up with it.