Here are the presidents who have been brought before national law

Democratic President Bill Clinton was brought before state law in January 1999. It was after the so-called Lewinsky affair where the president had a sexual relationship with Monica Lewinsky who worked as an assistant in the White House.

It was not the relationship in itself that caused Clinton to appear before state law but instead the lie when he said under oath "I have not had a sexual relationship with that woman".

In the Senate vote, a large majority of Republicans voted for him to be guilty. But at the same time, all Democrats and even a few Republicans voted for him to be innocent. Although all Republicans had votes for Clinton, they had not been able to reach the 67 votes required for the presidential election.

Andrew Johnson was vice president of Abraham Lincoln when the latter was murdered. He took office as president after the assassination - and that led to a shaky presidential term. Johnson was a Democrat and Lincholn Republican. Congress had a strong overweight of Republicans who did not want to see Johnson as president.

Formally, Johnson was brought before state court after he deposed Secretary of War Edwin Stanton. It was a violation of a newly enacted law that Congress voted for just to prevent Stanton from being dismissed.

But Johnson, too, passed during the Senate vote. All Democrats voted for his innocence. The final decision came when a number of Republicans also voted with the Democrats. Johnson was saved by a single vote margin.

Richard Nixon had never before a national court before he resigned in August 1974. On the other hand, he is believed to be the only president to date who could possibly also have been swept by the Senate.

The background was the so-called Watergate scandal. Five people had been arrested on suspicion of breaking into the Democrats' headquarters in the Watergate office complex. The motive for the break-in is believed to have been to obtain information before the presidential election in 1972. Several of the president's employees were involved and afterwards the president actively sought to silence the whole scandal. Among other things, calls were intercepted in the White House.

When it became clear that he would be put before the national court, Richard Nixon resigned himself.