As prescribed by the US Constitution, the three branches of government (executive, judicial, and legislative) are separate from one another and have power to decide on issues only within their own realm of authority. The system of checks and balances tries to guard against absolute power, in other words, to make sure that no one branch or individual in the government can override and take over the authority delegated to the other branches. The following are the highest levels of each governmental branch in the US: the President of the United States (executive); the US Supreme Court (judicial); and the United States Congress (legislative, consisting of two chambers: the US House of Representatives and the US Senate). In addition to the federal government, the principle of the separation of powers and the system of checks and balances are also built into lower-level (e.g. state, city-wide etc.) governments. The separation of powers means that no one government branch may exercise absolute power and that they are independent of one another (for example, the same person cannot be a US Senator and a US Supreme Court judge at the same time). Checks and balances is the system in which the different branches of government balance each other out. Although their mandate and responsibilities are different, this system tries to ensure that no branch of government exercises power over the others. For example, decisions made by Congress can be vetoed by the President, which can in turn be overturned by a 2/3 majority vote of both houses of Congress.