Its extremely hard to demonstrate corrupt intent for obstruction when there was no underlying crime.

Firing Mueller/Comey for explicitly political purposes is not obstruction of justice. Firing either because he knows the whole investigation is pointless and he did nothing wrong is not obstruction. You would have to show that the president took these actions solely to obstruct the investigation from reaching a likely conclusion that would cause him legal exposure. It's hard to demonstrate that when the bulk of the report focuses on the fact that the investigation was in fact a waste of a few tens of millions of dollars.

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