Forty years ago this week Richard Nixon resigned as president of the US, an epochal event. He thereby staved off almost certain impeachment and conviction by Congress for “high crimes and misdemeanours”, the standard laid down in the constitution, stemming from the botched burglary of the Democratic party’s offices in the Watergate building in the summer of 1972.

The word impeachment is abroad again, this time against President Barack Obama and emanating from the most radical right in and out of Congress. There is now a lawsuit pending, known as “impeachment lite”, brought by the Republican majority in the House of Representatives which accuses him of violating the constitution, specifically by unilaterally delaying implementation of the mandate on employers, part of his landmark health reform act, but generally, to be frank, because they cannot stand his guts.

In the intervening years, there was an actual presidential impeachment trial, of Bill Clinton, for lying under oath in sworn testimony over his sexual relationship with Monica Lewinsky, the White House intern. He was acquitted by the Senate. Only one other president in US history, Andrew Johnson in 1868, had previously been impeached, surviving by one vote in the Senate.