When answering this question, there are three levels of government to focus on: local, state, and federal government. Sub-national governments are comprised of local and state governments. The Constitution of the United States provides for a separation of powers to exist between state and federal governments. The founding fathers wanted to make sure that American citizens always had representation and a voice in government; many people believe sub-national governments ensure that citizens' voices are heard.
Likewise, consider how large the United States is. What would government be like if there was only one federal level? Would citizens be represented well or at all? Also, consider how each state has its own unique concerns, problems, and culture; the rules or guidelines that work well in one state may not work as well in another. Sub-national governments exist to help each state address its own needs.
However, there can be disadvantages to having so many levels of sub-national government in the nation. The amount of time spent on establishing, checking, amending, and defending the rules, regulations, laws, and policies of each level is tremendous. Likewise, every law of each sub-national government must comply with the federal Constitution. Citizens can be overwhelmed with how to get the help they need with many levels of government. You can research the effectiveness of sub-national governments. Do bureaucrats accomplish much? Do various levels contradict one another?
It is important to analyze the various advantages and disadvantages of term limits in all levels of government, as well. You could research the rules on term limits for federal officials in the Constitution. For example, only the president has term limits, with some caveats. Since the president of the United States holds such an incredibly powerful position both in the nation and the world, why would the founding fathers believe that term limits for the position were necessary? What about other federal officials?
Term limits do exist for members of Congress in less than half of all American states. Thus, you might want to consider if term limits are necessary to prevent members of Congress from gaining too much control over many years in Washington, D.C. Some Americans believe that corruption, bribery, party politics, and unfair practices become too common when many of the same members of Congress are in office year after year. However, you should also consider what the effects of term limits might be: would members of Congress have enough time to accomplish true change if their time was limited? This consideration would also be relevant to local officials.
You may explore the judicial branch at all levels, also. At the federal level, members of the US Supreme Court do not have term limits. Justices can serve for life, as long as they are mentally and physically capable. How does that affect decision-making over the years if there is not much change in the Court? Why did the founding fathers decide this for the Justices? Some people believe that since the US Supreme Court is the highest Court in the land, handling the most difficult, relevant, and poignant cases, then stability of the Justices is paramount. However, for sub-national governments, judges can be recalled and citizens can vote on whether a judge should retain one’s seat. You can focus on the impacts of these recall options.