Impeachment as the only means of removal shouldn't preclude other trials
The Nixon DoJ had the opinion that a sitting President shouldn't be on trial as that would interfere with their Executive duties, so their guidelines for no indictments.
That's not been tested, but clearly Clinton wasn't protected and can anyone imagine him getting away with a blanket refusal to reply?
While the Constitution is pretty clear that Impeachment or 25th Amendment are the ways to remove a President or transfer his powers, there is no language that blocks prosecution while in office. Given the amount of effort being expended on his obstructive behavior, it shouldn't be argued that he couldn't mount a vigorous defense while serving in office.
With modern technology and the work schedule of the current resident, house arrest or ankle monitored sentencing would not keep him from conducting official business and he could serve any custodial time when out of office.
That way, the truth could be discovered and judged, then Congress could decide whether he would be allowed to lead the country.