What Mr. Trump has done in the Ukraine is much, much worse than Nixon's action in Watergate. Trump and Nixon shared two high crises. Mr. Trump added a third.
Mr. Nixon's campaign team carried out a robbery at the Watergate apartment complex to get dirt on the Democratic party. Mr. Trump asked the Ukraine government to provide dirt on the Democrats in two areas: Hillary Clinton's computer server and Joe Biden's son.
Mr. Nixon and his staff tried desperately to cover up their crimes; an obstruction of justice. Mr. Trump has resolutely put pressure on members of his staff and on members of the wider administration to refrain from responding to Congressional subpoenas; an obstruction of justice.
In addition, Mr. Trump undermined US policy goals by withholding military aid to Ukraine while it was under ongoing attacks by Russia; this is treason, the highers of crimes.
Mr. Trump should be impeached. He should be tried in the Senate. He should be removed from office.