If you're so ignorant of the law as to NOT know who Blackstone was, what he said or how he ties into the Constitution, you never WILL understand the words "Republican form of government".
FYI- George Tucker
Tucker wrote poetry, political satire, tried his hand at drama, but is known best for his edition of Blackstone's Commentaries and his other legal commentaries, including View of the Constitution, one of the first extended commentaries on the newly ratified Constitution. He is sometimes referred to as the "American Blackstone" for his Americanized version of a multi-volume of Blackstone's Commentaries on the Laws of England.
The law books that Abraham carried around with him as he was studying for the bar included Blackstone's commentaries.