Not a lawyer, but here's my understanding...

Criminality isn't required for impeaching a President. Additionally, committing a crime isn't always grounds for impeachment.

I guess the underlying question is about impeachable offenses rather than criminality.

What's an impeachable offense?

Article II, Section 4 of the US Constitution states:

"The President, Vice President and all civil officers of the United States, shall be removed from office on impeachment for, and conviction of, treason, bribery, or other high crimes and misdemeanors."

Source: https://www.law.cornell.edu/constitution/articleii

"...founders wrote the impeachment clause to be broader than criminal activity. Many crimes are not impeachable (jaywalking, for example). Other activity isn’t necessarily criminal but is obviously a basis for impeachment (not defending the United States against a foreign attack)."

Source: https://www.nytimes.com/2019/09/25/opinion/trump-impeachment...

Did Trump commit treason?

"Under the U.S. Constitution, a person is guilty of treason if he or she goes to war against the United States or gives “aid or comfort” to an enemy. Treason is the only crime specifically defined by the Constitution."

"There is not a treason case to be made against Trump because the United States is not at war with Ukraine or Russia, said Paul Rosenzweig, a former federal prosecutor in Washington who worked on the special counsel investigation into Bill Clinton."

Source: https://www.reuters.com/article/us-usa-trump-whistleblower-c...

How about bribery?

"A federal law, known as the bribery statute, makes it a crime for a public official like Trump to corruptly request a thing of value in return for being influenced in the performance of an official act."

"In an impeachment investigation, House members are not required to adhere to the definition of bribery in the criminal code and can define the term more broadly to encompass corrupt uses of presidential authority for personal gain, legal experts said."

"Rosenzweig said bribery could potentially be one of the “articles of impeachment,” or charges, returned against Trump if the House takes that step."

Source: https://www.reuters.com/article/us-usa-trump-whistleblower-c...

And “high crimes and misdemeanors”?

"According to several constitutional lawyers, “high crimes and misdemeanors” is a purposefully vague term and can be defined by members of Congress."

"Writings by the nation’s founders make clear that they were concerned about presidents abusing the public trust, said Rosenzweig, now a senior fellow at the libertarian think tank R Street Institute."

“The founders spoke about things like promising pardons to your friends to protect your own criminality,” said Rosenzweig. “They spoke about things like people being beholden to foreign governments. They spoke about profiting from the presidency.”

"Some legal experts say there is already a strong impeachment case against Trump based on what is publicly known about his July 25 phone call with Ukrainian President Volodymyr Zelenskiy."

Source: https://www.reuters.com/article/us-usa-trump-whistleblower-c...

So did Trump commit an impeachable offense?

“Impeachable misconduct entails a president’s serious abuse of power and a serious abuse of public trust,” said University of North Carolina Law professor Michael Gerhardt.

"He said based on what has been reported so far, “President Trump’s call did both of those things. It was an abuse of power because he used his position to benefit himself and not the country. It was a breach of trust because Americans trust their president not to engage in self-dealing, either through steering businesses to line their own pockets or through conspiring with or coordinating with foreign powers to intervene in American elections.”"

Source: https://www.latimes.com/politics/story/2019-09-25/trump-ukra...