Once again all evidence points to Trump being a very stupid man. Most rich people understand that the price of running for public office is scrutiny, the more intense the higher the office, and most stay away, preferring to skulk in the shadows and pull the levers (e.g. Koch network).

He can't bluster his way out of it. There's a logical progression from the question of collusion to the question of undue influence, and Trump's large-scale entanglements with Russia compel Mueller to investigate.

Journalists have made casual reference to comparing the sale price of real estate Trump and family sold to Russian oligarchs, against fair market value. To put it bluntly, they're dancing around the possibility of money laundering, on a grand scale that, AFAIK, can only be accomplished with real estate transactions. Transactions whose existence would leave the participants open to blackmail. Hell yes Mueller will investigate if the trail takes him into apex corruption like that. Potential Russian leverage over Trump is an effin national security matter.

Trump being a Dunning-Krueger-afflicted political neophyte, I wonder: Did he not think to run opposition research on himself?