Article IV, Section 4 requires the federal government to guarantee each state a republican form of government and protect against invasion or domestic violence. Following the Civil War, Reconstruction Congress used this clause to transform former slave states, excluding representatives from governments it deemed unrepublican. But in Luther v. Borden (1849), the Supreme Court declared these questions "nonjusticiable," meaning courts won't enforce the clause—only Congress and the president can. Chief Justice Roger Taney ruled it rests with Congress to decide what government is established in a state. When Georgia challenged Reconstruction laws in Georgia v. Stanton, the Court treated Congress's actions as final. The Court has also refused to strike down direct democracy tools like ballot initiatives under this clause. Today, scholars debate whether Congress could use its exclusion power to deter voter suppression, but the political question doctrine still blocks most lawsuits seeking judicial enforcement.