Second terms often marked by scandal

Worst of all was Republican Richard Nixon, forced to quit after his administration was behind a burglary at Democratic offices in Washington's Watergate hotel before his re-election in 1972. The facts were not revealed until the following year.

In August 1974, Nixon resigned to avoid impeachment, only after his vice president, Spiro Agnew, resigned in the face of income tax evasion charges.

Democrat Bill Clinton, easily re-elected in 1996, was impeached but stayed in office. He was accused of perjury in trying to cover up his affair with White House intern Monica Lewinsky.