My theory is that Obama weaponized pretty much every federal agency to use against his enemies, and to try to take down Trump. Once Hillary got elected, nobody would ever find out his involvement. The Mueller investigation found nothing because there never was anything to find, and they knew it because Trump had been under surveillance for some time.
The Mueller probe will die a silent death because if Obama were to be shown to be the criminal that he is, Ferguson Missouri would look like a campfire. Nothing will happen here. The investigators are covering both Obama's ass and their own complicity. People like Manafort got caught up in it by doing what political folks normally do.