Which scenario is avoided because the constitution contains the supremacy clause?

The correct answer is D) a state passes a law that contradicts the 19th Amendment.

The scenario that is avoided because the Constitution contains the supremacy clause is "a state passes a law that contradicts the 19th Amendment.

The supremacy clause clearly states that in the case where state law conflicts with federal law, it is the federal law that has priority. So the clause was created in case there was any significant conflict between the states and the central government.

The other options of the question were A) the federal government amends the Constitution to expand citizenship rights to a new group. B) one branch of government becomes more powerful than the other. C) it becomes unclear whether transportation is the responsibility of the federal government or a state government.

four sitting presidents have been assassinated while in office but the first was abraham lincoln,