It's not the severity of the crime which makes it high, but it damn well better be a crime. Democrats haven't been able to come up with one despite turning themselves and the country into pretzels.
And Trump's tax returns from the past and his dalliances from the past and why he named his son "Barron" are all completely irrelevant, as is everything else he's done while not in office. Those things matter only at election time.
Here's Betsy:
At the 1787 Constitutional Convention, the framers considered grounds for impeachment. On Sept. 8, George Mason suggested that bribery and treason were too narrow, and proposed adding "maladministration." But James Madison objected, explaining that "so vague a term will be equivalent to" saying the president serves at the pleasure of the Congress. The framers did not want to duplicate the British system, which made the executive dependent on Parliament. Mason's idea was dropped, and the framers instead agreed to the more specific term, "high crimes and misdemeanors," where "high" meant offenses committed while in high office, such as embezzling public funds.
