The Impeachment Process Historically and Today

What has impeachment meant in the past and how has it been used, or almost used, historically? Given the results for the November 2018 mid-term elections, the revelations by the Mueller Special Counsel, and the inquiry into Ukraine, what are the odds we are looking at impeachment now? The Constitutional requirement for a two-thirds supermajority in the Senate sets a very high bar for the removal of the President. On the other hand, the Republic has never seen anything remotely like the Trump Presidency.