(i) The investigation was for collusion, not obstruction
Rosenstein also gave Mueller the power to investigate "any other matters within the scope of 28 C.F.R. § 600.4(a)" — including perjury, obstruction of justice, destruction of evidence, and intimidation of witnesses.
(ii) A sitting president cannot obstruct justice
The idea that a president can’t obstruct justice died with King George III, with a brief attempt at revival by Richard Nixon.
(iii) A sitting president cannot be indicted
Professor Tribe argues, very roughly, first that it is imperative that the Constitution be construed to permit indictment
Your cynicism is duly noted as it should be in consideration of current status of significant players in this drama. However, it also has to be noted first, SCO has purview outside the strict limitation of investigating collusion. Second, despite the fact a president has wide ranging powers, he could conceivably break the law by ordering acts which are illegal in other contexts. Third, to argue a sitting president cannot be indicted is tantamount to saying a sitting president is above the law.
My prediction ... SCO will report there was collusion (conspiracy) between Russian agents and the Trump campaign. There will be people named.
SCO will report Mr Trump maintained a pattern of obstructing justice of the underlying crime of collusion (conspiracy) with elements of the Russian government.
SCO will not report an indictment of Mr Trump in deference to current DoJ protocols.
Now the reality check ... Republicans will whitewash the report. DoJ will not prosecute based on report. There will be no impeachment proceedings in Senate. Blanket pardons will be issued. No political repercussions for Mr Trump and his gang of corrupt conspirators.
If this doesn't provide damaging fodder for a presidential campaign, then political operatives are not doing their job. I can not imagine not arguing a president of the United States was arguably acting on the behalf of the Russian government while sitting in the WH. Even Trump supporters can see how that would be deleterious to the security of the United States.
But I dunno. I also believe a huge chunk of Americans are, and I won't mince words, stupid.