The legislature, Congress, is elected by the People (and per the Constitution, the States, prior to the 17th Amendment). The legislature within the constraints of the Constitution, writes laws and sets policy. If members of the other two branches do not perform as expected, or extra-constitutionally, they may impeach, try (or not), and convict (or not) members of the other two branches. Conviction could lead to penalties of severance, up to imprisonment, and everything in between.
The judiciary, Courts - Judges are appointed by the executive branch with the advice and consent of the legislature. Though the executive appoints, the legislature must confirm, and has the final say in the appointment of judges. At the state and local levels, judges may be elected by the People. Judges try cases where the law has been broken. The judge does does not determine guilt or innocence. That is done by a jury of citizens. The jury may find 1 of two verdicts; guilty, or not guilty. Judges then set the penalty within parameters prescribed by the law. If the judge feels the law is unconstitutional, or the defense files a motion, the judge may render a verdict of acquittal. In any event, that verdict may be appealed to higher courts, all the way to the Supreme Court, where, ultimately, the law will be judged, and either upheld or struck down. The judiary also hears civil disputes, which are judged within the confines of the law, and the Constitution.
The executive- This includes the President (as well as governors and mayors), and Department Secretaries and Agency heads appointed with the advice and consent of the legislature, as well as the entire “civil service” and the military. The President is elected by the States (the Electoral College), with the advice and consent of the People. Governors and mayors are elected by the People. The executive branches sole authority is to enforce and prosecute the laws of the legislature, and execute policy pursuant to the will of the legislature.
