Chase was charged with abusing his judicial power. Johnson was charged with abusing his presidential power. But this President is charged with criminal behavior having nothing to do with the actual conduct of his office. Simply put, the senators will be asked to decide whether the President's lying about his sex life, even under oath, is a sufficiently grave threat to the Republic to warrant the cancellation of a presidential election, or whether such alleged misbehavior should be left to ordinary criminal law. I don't think the legal issue is close.
Perjury is a terrible thing.
So is obstruction of justice. But you don't need the nuclear weapon of impeachment to deal with either charge, unless the criminal behavior is connected to abuse of official power. Punishing personal wrongdoing is what the criminal courts are for. There's a rumor that a sealed grand jury indictment has already been issued by Ken Start against the President, to be opened the day he leaves office. The real risk posed by the Republicans' irresponsible effort to remove Clinton from office is that it degrades the meaning of high crimes and misdemeanors by allowing political opponents to focus on private wrongdoing instead of public need as a pretext for overriding popular electoral mandate.