Article IV, Section 4 - Daily Border Invasion

President Obama is suing the State of Arizona for passing a law about illegal immigration.

If given the responsibility of arguing for Arizona's law, I would simply say:

"Your honor, Article IV, Section 4 of the United States Constitution."

If the judge asked for an explanation, I would read the passage to the court:

Section 4. The United States shall guarantee to every State in this Union a Republican Form of Government, and shall protect each of them against Invasion; and on Application of the Legislature, or of the Executive (when the Legislature cannot be convened) against domestic Violence.

If there is any debate on this quotation, I would add the oath of office for federal officials, including the House and Senate:

I do solemnly swear (or affirm) that I will support and defend the Constitution of the United States against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; that I take this obligation freely, without any mental reservation or purpose of evasion; and that I will well and faithfully discharge the duties of the office on which I am about to enter: So help me God.