Supreme Court Justice Sandra Day O’Connor’s decision to retire left President Bush and his advisers with a major decision to make, one that will affect the future of U.S. politics as impacted by the judicial branch.

Though the Supreme Court is not a partisan body like the legislative and executive branches, political ideology is one of the major considerations of any president in choosing a Supreme Court nominee, and personal political beliefs affect the rulings of each justice.

So, just how did the justices of the Supreme Court become so important in U.S. law, government and politics?

Part of the answer is that they were given that power by the Constitution. However, much of the court’s power was granted by the early justices themselves.

In 1803, the case of Marbury v. Madison went to the Supreme Court. Just before his term ended, President John Adams attempted to fill a number of court vacancies with fellow Federalists. However, when Thomas Jefferson (a Democratic Republican) took office, many of Adams’ commissions for judgeships had not yet been delivered. Jefferson’s secretary of state, James Madison, had no intention of delivering the commissions, either. William Marbury then sued Madison in an effort to force the delivery of his commission as justice of the peace.

Supreme Court Chief Justice John Marshall was in a tough spot. If he ordered Madison to deliver the commission, he knew the order would be ignored. However, if the court did not order Madison to deliver the commission, it would appear that the Federalist judges had acted out of fear. Either option would weaken the court.

In a craftily written majority opinion, Marshall avoided both damaging outcomes while strengthening the power of the court. Marshall concluded that the Judiciary Act of 1789 (which gave the Supreme Court the right to order Madison to issue the commissions) gave the Supreme Court power that exceeded the authority granted by Article III of the Constitution.

Marshall’s decision set the precedent that the Supreme Court has the ability and right to interpret the Constitution, and to declare acts of Congress or the president unconstitutional. In effect, Marbury v. Madison made the Supreme Court as prominent a body in government and law as the executive and legislative branches.

Because of Marbury v. Madison, the Supreme Court justices retain great influence, challenging presidents to nominate not only the greatest legal minds in the country, but also justices with ideologies similar to their own.