Impeachment is set forth for bribery, treason or high crimes and misdemeanors. I think the argument could be made that bribes taken while Vice were then reciprocated during the Presidency. Certainly the Ukraine money funnel seems to be indicative of that. Also, the line that’s currently being drawn to Granholm’s visit with China being followed up with the depletion of our Strategic Oil Reserves to China might be indicative of treason.
Except we are not at war with China (No declared war!) so, it doesn’t meet the Constitutional definition of treason. Sedition, more bribery, possible violations of the Espionage Act, failure to register as a foreign agent, etc. yes but doesn’t meet the treason threshold.
The Founding Fathers deliberately set the bar for treason very high!