Double Jeopardy and Impeachment

JOAQUIN BERNAS in his PDI Commentary today addresses a question I've been discussing in Social Media recently:

One question that must also be asked is whether there is a difference between the meaning of “Guilty” as found in a judicial decision and “Guilty” as found in an impeachment conviction when they are dealing with offenses of equal gravity. 

There is a difference in the result. When a court convicts for treason or bribery, it makes a judgment that the person must make amends through loss of life or liberty. When an impeachment court imposes removal from office, it makes a judgment that there are compelling reasons for shielding the nation from further harm but leaving retribution to the judgment of a court. For that reason, prosecution after conviction on impeachment does not constitute double jeopardy. However, the needed quantum of proof for either criminal conviction or impeachment conviction are not far from each other, if there is a difference at all.

I am puzzled and nonplussed by the concluding statement of Fr. Bernas. for if there were no difference at all in the quanta of proof to convict on impeachment trial AND to convict on criminal trial, why should judgment be limited to removal from public office and not proceed to criminal fine or imprisonment?

I agree of course that it is NOT double jeopardy for impeached Constitutional officers to be tried possibly twice for the same offense: once in the Senate, and upon removal through the regular Courts. But I also don't agree that there ought to be a double burden of criminal prosecution on the state.

It would seem only most reasonable to conclude that the quantum of evidence for conviction upon impeachment trial ought not to rise to the level of technicality and compliance that a later criminal procedure will surely impose any way.

I suppose one important point to uphold is that conviction upon impeachment is not guarantee of conviction upon any subsequent criminal action that might ensue.