Obstruction IS a crime. On it’s own. Without any underlying qualifications.
If you knowingly worked to obstruct investigation you are guilty, period.
Investigation of what?
This isn't a buffet. You don't get to question a number of things until
you find a lie. You don't get a special counsel to find a crime.
If the investigation is for collusion then the questions will be limited
to collusion. If Mueller doesn't agree then he is forced to put Trump
before the Grand Jury He doesn't get to ask the questions then and
he cannot tell the Grand Jury that they have to ask trick questions trying
to find a lie because there is no collusion