The public impeachment inquiry hearings this week usher in a rare and momentous occasion in American history as Congress debates whether to remove a president from office.

There are consistencies in the process — televised hearings, partisan rancor and memorable speeches — but each impeachment process also stands alone as a reflection of the president, the Congress and the times.

Even if the two most recent impeachment proceedings — against Presidents Richard Nixon and Bill Clinton — offer instructive clues about the path ahead, there are notable differences in the case surrounding Donald Trump.

A look at then and now:

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THEN: During the Clinton impeachment, the House held no serious hearings because the independent counsel, Kenneth Starr, had delivered dozens of boxes of evidence with recommendations for charges. Even during the Nixon proceedings decades earlier, lawmakers were considering evidence gathered through months of investigations by specially appointed prosecutors — first Archibald Cox and later Leon Jaworski. In both cases, the impeachment proceedings followed extensive law enforcement investigations.

NOW: The House Intelligence Committee has taken on the primary role of assembling a case against Trump, with no supplemental Justice Department investigation. These impeachment proceedings are unfolding simultaneous to the investigation itself.