He acknowledges, as does St Thomas, that no subject has the right to overthrow the legitimate, constitutional monarch or government.
And the monarch does not become "illegitimate" simply because some of his subjects begin to think that he is.
If it can be shown that the ruler is an usurper, who made himself king or governor without regard to the lawful constitution of the state, then he can be overthrown and the real king or governor restored.
Restoration is legitimate but revolution is always evil.
And even restoration may only be attempted if the other just war criteria are met e.g. proportionality or likelihood of success.
St Thomas says this of rebellion:
" If the excess of tyranny is unbearable, some have been of the opinion that it would be an act of virtue for strong men to slay the tyrant and to expose themselves to the danger of death in order to set the multitude free (5). An example of this occurs even in the Old Testament. For a certain Aioth slew Eglon, King of Moab, who was oppressing the people of God under harsh slavery, thrusting a dagger into his thigh; and he was made a judge of the people (6).
 But the opinion is not in accord with apostolic teaching. For Peter admonishes us to be reverently subject to our masters, not only to the good and gentle, but also to the froward: “For if one who suffers unjustly bear his trouble for conscience’ sake, this is grace” (7). Wherefore when many emperors of the Romans tyrannically persecuted the faith of Christ, a great number both of the nobility and the common people were converted to the faith and were praised for patiently bearing death for Christ. They did not resist although they were armed, and this is plainly manifested in the case of the holy Theban legion (8). Aioth, then, must be considered rather as having slain a foe than assassinated a ruler, however tyrannical, of the people. Hence in the Old Testament we also read that they who killed Joas, the King of Juda, who had fallen away from the worship of God, were slain and their children spared according to the precept of the law (9).
 Should private persons attempt on their own private presumption to kill the rulers, even though tyrants, this would be dangerous for the multitude as well as for their rulers. This is because the wicked generally expose themselves to dangers of this kind more than the good, for the rule of a king, no less than that of tyrant, is burdensome to them, since, according to the words of Solomon: “A wise king scattereth the wicked” (10). Consequently, by presumption of this kind, danger to the people from the loss of a good king would be more probable than relief through the removal of a tyrant.
 Furthermore, it seems that to proceed against the cruelty of tyrants is an action to be undertaken, not through the private presumption of a few, but rather by public authority".
[St Thomas Aquinas, De Regimine Principum (On Kingship), quoted in Dino Bigongiari, ed., The Political Ideas of St. Thomas Aquinas, New York: Hafner Press, 1953, Book I, Ch. Six, 49-51. St Thomas cites the following sources in the extract: (5) Cf. John of Salisbury. Policraticus viii. 18, 20. (6) Judges iii. 14 ff and see Policraticus viii. 20. (7) 1 Pet ii. 18,19. (8) Acta Sanctorum Septembris, vol VI, 308 ff. (9) IV Kings xiv. 5, 6. (10) Prov xx. 26.]
The Roman Catechism of the Council of Trent teaches the same:
"If we sometimes have wicked and unworthy officials it is not their faults that we revere, but the authority from God which they possess. Indeed, while it may seem strange, we are not excused from highly honouring them even when they show themselves hostile and implacable towards us. Thus David rendered great services to Saul even when the latter was his bitter foe, and to this he alludes when he says: ‘With them that hated peace I was peaceable. However, should their commands be wicked or unjust, they should not be obeyed, since in such a case they rule not according to their rightful authority, but according to injustice and perversity’ ".
[On the Fourth Commandment]
The symbolism is dual: evil men claim the right to judge and condemn Christ the King of Kings, God Himself, the highest authority and, in so doing, give God the opportunity to provide an image of kingship forever new, namely, that kings wear the crown as Christ worn the thorns, as a cross, a duty, a burden, for the sake and service of his subjects. Christ becomes the supreme symbol of all those who suffer for the sake of right and justice - especially rulers who are rebelliously overthrown by their own subjects, for rebellion is sin and sin is rebellion.