Outside evidence of real collusion, there are two obvious ways that the Mueller investigation could go thermonuclear. One is if Jared or Don Jr. made the same mistake as Michael Flynn and didn’t tell the truth to FBI agents. The other is if Mueller begins probing Trump’s finances in earnest. Trump would likely not stand for either.
If Jared or Don Jr. ends up in Mueller’s clutches, there is a relatively easy solution for Trump — pardons. Having to pardon his son-in-law or son would be very awkward to say the least, but you can see how Trump would make the case for it, “This is a good kid who was just trying to protect my interests and got in over his head,” etc., etc. There might be enough sympathy for this argument out there that Trump wouldn’t necessarily pay a major political price.
But if Mueller starts going after Trump’s finances, it’s hard to see any solution from Trump’s perspective other than firing Mueller — and that would be an enormously consequential act that would probably rock his presidency to its foundations. The latest news, by the way, is that Mueller has subpoenaed Deutsche bank records.