If that is true, why does the constitution outline the rules? Treason, Bribery, or other high Crimes and Misdemeanors are the only reasons outlined in the constitution for a basis for impeachment. Not whatever the Democrats decide is a good reason minus any crime. If they had uncovered even a misdemeanor, then there could be a political basis, but as far as we have seen - not even that has been found.
High crimes originally were not meant to be criminal offenses of a more serious nature but those offenses engaged in by "high" or public officials that were supposed to act according to their oath of office, unlike what ordinary citizens were subject to.
IOW, high crimes did not necessarily mean felonies but any offense committed by officials in "high" positions of public trust. Offenses against the oath of office.
And misdemeanors did not necessarily mean crimes of a lesser nature but any offense that the House saw as dereliction of official duties of the "high" office.
Impeachment for misdemeanors embraces serious wrongs of a "political" nature like misconduct, contempt of congress or abuse of power, as well as more common pedestrian offenses punishable by ordinary criminal law.
So the House democRATS could bring impeachment charges against Trump for directing his employees to not testify in front of the House committees when called upon or subpoenaed.
Don't be looking for some criminal misdemeanor that Trump has committed as the only reason they can impeach him. It could be for simple doing something in office the House considers to be misconduct, like his outrageous behavior or Tweeting constantly.