The lead prosecutor in the impeachment trial of former US president Donald Trump said Tuesday his case was based on "cold, hard facts," and proceeded to present video evidence that Trump incited violence on January 6.

The historic second impeachment trial of Trump began with debate on whether trying an ex-president is indeed constitutional.

Lead House impeachment manager Jamie Raskin, a lawmaker from Maryland, told senators he would not bore them with professorial speak, saying: "You will not be hearing extended lectures here from me because our case is based on cold, hard facts."

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