Trump tried to obstruct justice, but because justice wasn't obstructed due to others, it'd be harder to present a case. Yeah, "total exoneration" there bub.
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Putting the ball in Congress' court is literally equivalent to doing and recommending nothing, though
The Mueller report indicated that the President abused his authority.
Which, without prompting any action or consequence without the approval of Congress, means literally nothing
If we had a Congress that obeyed the Constitution, it could mean something. What Mueller is saying is that Congress is the venue for correcting this. And he is right. Proving obstruction is much harder in court. In Congress, the bar is lower.
And back to the original point, despite the White House saying
"President Trump has been fully and completely exonerated yet again.", the report clearly indicates Trump abused his power. This won't lead to impeachment, but the significance of the report saying as such is very high. I understand your statement in indicating, 'well, so what, nothing will come of it'... but it is a thorn directly into Trump and refutes their claim that Trump was exonerated.
Won't stop them from saying it though.