Like talk to Mueller. If he speaks to Mueller for thirty minutes, it's likely that he'll lie at least a dozen times.
As I've said since Trump's refusal to show his taxes, follow the money. Just the easy parts are damning. We know for a fact that VTB gave Trump Toronto about $150M. We know for a fact that a Putin lackey paid $40M over asking price for a Trump property in FL with no other bids on the table for months. We know for a fact that a major Russian money-laundering scam operated out of Trump Tower. We know for a fact many Russians paid cash for Trump properties. We know for a fact Devos' brother met with a Putin partner in the Seychelles. We know for a fact that Jared met with VTB during the transition. We know that Trump's sons said they got their money from Russia.
These are just a few. There are obviously more that we don't know. Hookers owe their pimps less than Trump owes Putin.
Lying to Muller or the FBI are not illegal activities that are going necessarily to bring down the Trump administration. Clinton got away with it, because the senate didn't think it rose to the level of an impeachment. I think that is what the you're only damned if did something really wrong comment refers to. Even money laundering and tax shenanigans prior to 2016 may not be "really wrong" enough to warrant impeachment.