[craigching]

Impeachment is a political process, not a legal process.

EDIT: To back this up, from Wikipedia:

  In the United States, impeachment is a remedial rather than penal process,[13][14]: 8  intended to "effectively 'maintain constitutional government' by removing individuals unfit for office";[14]: 8  persons subject to impeachment and removal remain "liable and subject to Indictment, Trial, Judgment and Punishment, according to Law