If I may contribute a single observation: In Dante's Divine Comedy, Satan is depicted occupying the centre of hell, his three mouths chewing on Judas, Brutus and Cassius. So Dante put those who betrayed Julius Caesar literally on the same level as the one who betrayed Christ.. That seems hard to reconcile with thinking the transition was a bad thing.

From what I know of the Carolingian renaissance, people like Loup of Ferrières had an anachronistic view of Roman politics, and therefore did not think historically. For instance, Ferrières invokes (in a letter of 846 to Charles the Bald) as a model the Roman Senate and the dilectio publica (the dedication to the common good) of people like Cicero, to which he explicitely refers and that we know he had read; but he seems to envision the Senate as a somewhat generic council, and he compares it to the Carolingian placitium (annual gathering of aristocrats and clergymen which discussed and approved royal lawgiving). Of course, the placitium, which presupposed the monarchical principle, was very much unlike the Senate of the Republic, but it was not considered too much of a problem.

My vague memories of courses on French politics during the Hundred Years' War would tend to indicate that it was pretty similar during the Late Middle Ages: the principle of the res publica was understood as a generic idea that was not linked to a particular regime. In that, we can say that Augustean propaganda on the “restauration” of the Republic was pretty successful: you could have a de facto monarch without endangering the substance of the res publica. I would tend to think that assimilation of anti-monarchic discourse of the Romans would happen a bit later, under the influence of the Reformation — the first public defenses of regicide were not written, I think, before the 15th century (there is a very good chapter on this in Roland Mousnier's L'assassinat d'Henri IV, but I don't think it was ever translated in English), and some of them used the models of people like Brutus and Cato.

Hello friend. During my studies about Machiavelli (albeit not being a Medieval figure per se) and his works, it seemed that he held in high regard the Republics as form of government. Moreover, he admired Rome has a state with virtue, which helped her conquering the world. Machiavelli thought that Caesar was responsible for the eventual fall of Rome. Caesar actions, such as stripping the Senate's legal powers) led to weakening the foundation upon which Rome's glory stood.