to accuse or charge with misconduct in office; to attempt to discredit.

[mmonk]

This is the definition of impeachment. The charges are called articles of impeachment which are gathered through investigations. The senate trial is not technically impeachment, it's a verdict on the charges. Therefore, congressional investigations into wrongful conduct concerning constitutional matters by an elected official is impeachment. It's important to know since there seems to be a misunderstanding of this and thus strange arguments made here by some. So those of us calling for impeachment get a little tired of responses such as "investigations first".