The next president is expected to name at least one new justice to the closely divided court.
Key decisions of this term show a willingness of some justices to reject political leaders' judgments.
The ruling, a victory for Exxon, reduced the $2.5 billion punitive damages to about $500 million.
In a 5-to-4 ruling, the justices decide child rape isn't a capital offense.
The US Supreme Court ruled 5 to 4 Thursday that those held in Guantánamo can challenge their detention.
Two high court rulings on Monday will complicate US efforts to prove certain crimes.
The Supreme Court allows a 2003 law dealing with 'virtual' child porn that some thought was too broad.