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.–Article IV, Section 4 of The Constitution

[W]e may define a republic to be, or at least may bestow that name on, a government which derives all its powers directly or indirectly from the great body of the people, and is administered by persons holding their offices during pleasure, for a limited period, or during good behavior. It is ESSENTIAL to such a government that it be derived from the great body of the society, not from an inconsiderable proportion, or a favored class of it; . . . It is SUFFICIENT for such a government that the persons administering it be appointed, either directly or indirectly, by the people; and that they hold their appointments by either of the tenures just specified[.]–James Madison, Federalist 39

Madison say a Republican Form of Government:

1. derives all its powers directly or indirectly from the great body of the people
2. is administered by persons holding their offices during pleasure, for a limited period, or during good behavior.
3. be derived from the great body of the society, not from an inconsiderable proportion, or a favored class of it
4. persons administering it (the government) be appointed, either directly or indirectly, by the people; and that they hold their appointments by either of the tenures just specified

There is reason to doubt that the Federal Government today meets Madison’s standard for a “Republican form of Government,” thus is unable and unwilling to guarantee that to the states.

1. The electorate is something less than “the great body of the people.”
2. Many hold office for no reason other than party allegiance, whether their behavior be good or not.
3. The wealthy class has undue influence.
4. Some elected officials hold office in spite of bad behavior.

I disagree with Madison’s condition of “limited terms;” I believe experience is important in government as in other human endeavors and that term limits alone are no guarantee of good behavior. Perhaps experience was less valuable in Madison’s time.