The most effective topic sentence for a paragraph in an essay about the checks and balances of political power in the United States federal government is: "The judicial branch has the following check over the legislative branch: courts can judge legislative acts to be unconstitutional."
This topic sentence is effective because it clearly states the main idea of the paragraph, which is the specific check that the judicial branch has over the legislative branch. It sets up the paragraph to discuss how the courts can declare legislative acts unconstitutional, thereby limiting the power of the legislative branch.
In the paragraph that follows, you can provide examples and further explain how this check works. For instance, you can mention landmark Supreme Court cases where the Court has struck down laws passed by Congress as unconstitutional, such as Marbury v. Madison or Brown v. Board of Education. This will help illustrate the concept of checks and balances in action within the federal government.
Remember to provide evidence and explanations throughout your essay to support your main points and give a comprehensive understanding of the checks and balances system in the United States government.