(Reuters) -John Roberts has served for two decades as the chief justice of the United States, a time when the Supreme Court has moved American law dramatically to the right.

Here is a look in chronological order at a dozen instrumental decisions by the court since Roberts, 70, was sworn in as the leader of the top U.S. judicial body on September 29, 2005.

DISTRICT OF COLUMBIA V. HELLER (2008)

The court decided that Americans have a right under the U.S. Constitution's Second Amendment to possess firearms in their homes in a ruling expanding gun rights. The 5-4 decision, written by Justice Antonin Scalia and powered by the conservative justices, overturned the District of Columbia's ban on handguns, a measure intended to combat firearms violence. Scalia rejected the view that the Second A

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