Laurence Tribe on Wednesday suggested that Democrats are now in possession of the “smoking Howitzer” with which to impeach President Donald Trump.

The Harvard constitutional law professor told CNN’s Anderson Cooper he believed House Speaker Nancy Pelosi (D-Calif.) was “wise to hold off” until last month to begin an impeachment investigation, after she had “what amounts to not just a smoking gun, but a smoking Howitzer.”

Tribe said Tuesday’s private congressional testimony of former Ukraine Ambassador Bill Taylor, who reportedly acknowledged that Trump had pressured Ukraine’s president to investigate his potential Democratic 2020 rival Joe Biden by withholding military aid to the country, was “dynamite.”

“This is just the most transparently clear abuse of power and an impeachable offense that I can remember in the history of the United States and I studied it pretty thoroughly,” Tribe added. “This makes the Nixon situation looks silly by comparison, this is way more serious.”

Check out the interview below: