Impeachment is a political process. The dangerous precedents have already been set, for Andrew Johnson and William Clinton.
The former was impeached for firing the Secretary of War without consent of the Senate, and refusing to reinstate Stanton in that position when it did not ratify the dismissal. Acquitted by one vote.
The latter was impeached for lying about inappropriate personal behavior, and obstruction of justice for witness tampering and impeding investigations. Acquitted.
Trump could be impeached by the House for a misdemeanor as inconsequential as littering in a national park. And the standard of proof for conviction in the Senate is not specified. It could be as low as "a police dog alerted on his hamburger wrapper" if his loyal contingent has 33 senators or as high as "we need to analyze, line by line, the source code for the video encoder of the camera that recorded the president dropping the wrapper on the ground, to ensure it has not been tampered with by terrorist immigrant caravans" if his contingent has 34 senators. It is not specified by the Constitution, so it is de facto determined ad hoc by the Senate and chief justice at the time of the trial.
It should be obvious that suspected crimes that are more severe than firing cabinet officials without permission, or covering up a political scandal--such as those imputed to Nixon during the Watergate burglary investigation, or suspected acceptance of foreign emoluments--should be impeached more readily. But as long as the Senate is needed to convict, and the burden of proof is not specified, then the House cannot realistically impeach, and expect a conviction with a president-supporting Senate in place, until the case against can meet the standard of "beyond even petty, unreasonable, and dubiously-contrived doubts". And that is solely so that when the Senate refuses to convict anyway, the evidence and the vote against conviction can be used against the party in subsequent election campaigns.
I have little doubt that the current president will be confronted by a stack of previously sealed criminal indictments on the afternoon of the next president's inauguration day. Those cases will be tried in courts with a fixed standard of proof--beyond reasonable doubt for criminal cases, and preponderance of evidence for civil cases.