Well, let’s construct a picture based on the known charges / deals at this point.
We have Flynn and Papadopoulus (sp?) both cutting deals to squeal about collusion during the campaign in order to save their hides for lying about it. Ok, politically damaging, but not particularly incriminating by itself. Note that the collusion at this time is known to be about lifting Russian sanctions, specifically with regard to anti-money-laundering rules.
But then you have Manafort & Gates, both indicted on “conspiracy against the U.S.” and “conspiracy to launder money”. Those are still in process, but they have much wider-reaching implications. If a clear conspiracy implicating Trump is found, especially if has to do with him being entangled in money laundering with Russia and conspiring to do the same, he’s really up the creek, and it doesn’t matter if he did it pre-presidency.
And honestly, the whole picture up to this point pretty clearly shows that the FBI is mostly chasing the money laundering aspect, because that’s the hardest one to evade (and it’s overwhelmingly probable that Trump has decades-long ties to Russian money laundering), so being able to link his actions in office to ongoing efforts to enrich himself and his family at the expense of America’s security and well-being is really big, and is independent of whether or not he actually accomplished his goals; the conspiracy and bona fide attempts to do so are enough.
Edit: I should also mention that an argument can be made that even if Trump is never indicted, the money laundering charges (which would involve his organization) are likely to be flexible enough to seize his organization’s assets, and since the laundering goes so far back historically, and penalties are DOUBLE the amount laundered (and remember that you only get to keep a smallish cut of the amount laundered!) and the statute of limitations only kicks in from the date the laundering is discovered… Well, he might stay out of prison, but he won’t be going back to any gold-studded apartments either. Between those penalties and any related IRS penalties (with massive interest!) that would be associated with this activity, he’ll be lucky to be able to afford a gold-spray-painted trailer by the time the screaming is all over.
