Many commentators have noted that proving that a President committed "high crimes and misdemeanors" is not the same as proving that the President committed a crime. The history of the drafting of the Constitution shows that the phrase "High Crimes and Misdemeanors" was adopted to cover a broad spectrum of wrongful acts that may not fit any statutory definition of a crime. A useful comparison might be the conduct of President Reagan, who was not impeached, and President Nixon, who was. "Impeachment" means the process by which the House of Representatives presents Articles of Impeachment, which is the equivalent of an indictment, before the matter moves to the Senate for trial or other proceedings.
There was support for impeachment against President Reagan for his violating laws passed by Congress, but ultimately no Articles of Impeachment were lodged. This may have been because of his popularity or because Congress did not see his conduct as bad enough. As for President Nixon, the Judiciary Committee approved three Articles of Impeachment against him, obstruction of justice, abuse of power and contempt of congress. Nixon ultimately resigned.
Nixon certainly did a lot more things than Reagan to justify impeachment. He was complicit in a break-in at the DNC. He attempted to cover up its involvement. He defied a Congressional subpoena. The Supreme Court ordered him to comply.
In Ronald Reagan's case, the Iran-Contra scandal senior officials who secretly facilitated the sale of arms to Iran which was the subject of an arms embargo (how ironic is that in today's world?!!!). The Administration intended to use the proceeds to fund contractors in Nicaragua in violating of a Congressional ban. Reagan was not taped and whether Reagan was involved was never proven.
What is the difference between what was done by President Reagan and what was done by President Nixon? Apart from the sheer number of things Nixon did, he was on tape and Reagan was not.
In Latin a significant distinction exists between malum prohibitum and malum in se. According to Wikipedia, malum prohibitum literally translates into "wrong as or because prohibited" and is a Latin phrase used in law to refer to conduct that constitutes an unlawful act only by virtue of statute. On the other hand, conduct that is "evil in and of itself" is malum in se. This raises the question of whether President Trump's conduct was malum prohibitum or malum in se.
In the Mueller Report we learned that his lawyer, Michael Cohen, testified that President Trump was aware of the payments made to women to keep quiet about their affairs with him. But if President Trump pressured Ukraine's President in a recorded conversation to investigate Joe Biden, while perhaps a campaign law violation, it seems to be much more than that. If he was withholding financing for Ukraine's defense, he may have been interfering with the foreign policy of the United States.
What makes the Ukraine situation different from Michael Cohen's implicating President Trump in a crime? Here, we have the President's own words recorded. This is significant. Former Deputy Attorney General Rod Rosenstein was accused of suggesting secretly recording Trump. It is a common practice of federal prosecutors to attempt to lock up their cases by getting the target to a meeting and then taping the conversation. President Trump "secretly" recorded himself. Do his words show his intent was Malum In Se, i.e. "evil in and of itself."