Remember how Nixon was charged with obstruction?

[Kablooie]

He was accused of obstruction by Democrats because there was a mountain of evidence but the Republicans weren't buying it.
It wasn't until audio tapes of Nixon openly ordering people to block the investigation to protect him that things turned around.

Obstruction of justice is not an easy thing to adjudicate. You have to prove intent without ambiguity.

We are close to that but Mueller states that most of the evidence is already in the public so unless he has more convincing damning evidence it's unlikely that the obstruction charge will go anywhere.