Campaign Finance Fraud was not among the items Special Counsel was tasked to investigate. Not named as such. What may come about as he investigated Russian Collusion with the President, and his Campaign, was within SC purview and so Special Counsel did look at various actors and their activity in that regard and found no actions rising to justify charges, beyond the persons who have already been charged. Most if not all negotiated pleas to such charges.
No charges directly involved the Republican Campaign, or persons acting on behalf of the Campaign for any charges.
The Russia Collusion investigation was found unworthy of further charges. The Campaign finance spin off investigations of individuals in Trump's orbit went nowhere, and so no charges were ever brought in that regard.
Special Counsel Mueller chose not to charge, and not to exonerate, regarding any supposed Obstruction Of Justice. Special Counsels and Prosecutors generally do not 'exonerate' under the U.S. System Of Justice. They bring charges if warranted, and no charge if no charge is warranted, and the Prosecutor is entrusted to make that determination.
Every Citizen is presumed Innocent, until proven guilty in a court of law. That is how the system works. I presume SC Mueller had his reasons, in the case of Obstruction Of Justice, not to make any recommendation. That decision was therefore left, within the U.S. Department of Justice, to the U.S. Attorney General.
Could be some of the other Prosecutors on Mueller's Team have strong feeling on one or more issues, which differ from Mueller, and still Mueller found no reason to bring a charge. Is this a bit of 'mischief' on Bob Mueller's part, to leave some 'balls in the air' to so speak, maybe a way to allow those seeking any shred of hope to cancel the results of the 2016 elections to flower?
Some believe that Mueller is not one to make mischief. Some believe he had satisfied his own commission with the findings he presented, to the best of his own ability, and just did not feel the same as some of his staff. Whatever.
Congress is free to investigate, should they bring Impeachment Proceedings.
The Executive Agencies are not under obligation to share Grand Jury Testimony or other evidence covered as Confidential in Mueller's Confidential Report to the Attorney General.