It is robust but it’s all built on TRUST. Like a fiat currency is. It’s built on the notion that those in the three branches will act in the best interests of their constituents and the nation as a whole (or the Constitution, writ large), as opposed to themselves or a small cadre or subset of America (those also in positions of authority). The danger of a lying tyrant king isn’t so much him, but that dozens/hundreds of others are supposed to keep him in check, not bow to him and put deference to him above deference to America’s interests. This is what oaths are for. They presume honesty, or enough honest people to overcome dishonest ones. In Nixon’s case the rot was largely confined to the executive branch. In Trump’s case, it’s infected all three branches. Hundreds of liars and cheats abandoning their oaths of office to, ironically, keep their offices.