In the midst of my reading of Bonhoeffer I dug into John Calvin to see what he had to say about opposing a tyrant. This is my summation of the last chapter of The Institutes of the Christian Religion (1559) on the matter:
Despite strong beliefs that kings and other leaders are chosen and ordained by God to rule, that rebellion is sinful, and that individuals have no right to regicide or tyrannicide, John Calvin in the final pages of his Institutes of the Christian Religion, states that “lesser magistrates,” other officials appointed or elected to govern, have the right and duty to check the tyranny of kings “as Constitutional defenders of the people’s freedom.”
“If they wink at kings who violently fall upon and assault the lowly common folk, their dissimulation involves nefarious perfidy, because they dishonestly betray the freedom of the people.... Let the princes hear and be afraid.”
“Obedience to man must not become disobedience to God.” "When a king exceeds his limits and has been a wrongdoer against men, he opposes God, and abrogates his own power."
"We have been redeemed by Christ at so great a price as our redemption cost him, so that we should not enslave ourselves to the wicked desires of men — much less be subject to their impiety." [I Cor. 7:23].