They can be investigated and held to account by Congress. That's what impeachment is. That's the whole point of having impeachment in the constitution.
If Congress fails to exercise its constitutional duty, then the problem lies with the specific representatives that place party above country.
We've seen it fail over and over. They won't investigate their own seriously, and even when they find the grossest violations of law, they cover it up.
The idea that there will be justice by the voters is laughable.
Playing devil's advocate, at least in part...
In practice, he cannot perform many of the duties of the office effectively - or perhaps at all - from jail.
The Constitution is the supreme law of the land, and it says he should be President (given the outcome of the process we had). The laws that say he should be in jail are subordinate to the Constitution and so rightly lose out in the minimum way practicable - a delay in sentencing.
...
I do have problems with some of what I've written here, but it seems like a sensible position that could be held unreservedly by someone who disagrees with me on a few questions of fact that do have a subjective component.
The reality is that we've codified that Presidents are largely unable to be investigated and or held to account by the legal system. There was no carve outs in the constitution at any point for anybody in government. This is a new, and probably fatal invention.