The Constitution gives us a procedure for handling a criminal president. The founders even considered the possibility that a president might beholden to foreign powers.
The procedure is this:
At the first sign of corruption, fraud, or a foreign influence in the election, Congress. . .
Thus the cause of our constitutional crisis isn’t a lawbreaking president.
A former president can, of course, be indicted and brought into a regular criminal court.
This is what the founders envisioned: Impeach, remove, indict, conduct trial.
Consider the problems with a trial: If he's found guilty, he’d have to be removed from office, which means a jury of 12 people would have the power to remove a president from office.
The other reason is that a trial would be a media circus. Good luck finding an impartial jury.
There are good reasons for that. What if a jury of 12 in a deep red state had been able to remove Obama from office?
Besides we have to follow the Constitution. No choice.