John Gruber, at Daring Fireball, on what the Russians most likely have on Trump:
“I don’t think it’s the infamous pee tape because even if real, the pee tape might not sink Trump. I think it’s money — that Trump’s entire company, and therefore his personal wealth, is held afloat entirely by Russian money and Putin could pull the plug on it with a snap of his fingers. But whatever it is, it seems clear there’s something they’ve got on him.”
Gruber again:
“I’ve been thinking for a few months now that the most powerful person in the world isn’t Trump or Putin but Rupert Murdoch. If Fox News turned against Trump — not against Republicans, not against conservatives, but only against Trump and his family — it would sink Trump’s presidency within months. Politically, Trump couldn’t breathe without the support of Fox News. Rupert Murdoch could make that happen.”
Pressing Pause 
The Russian money connection is a very likely scenario. It would explain why he has refused to show his income tax returns
I can’t imagine what would prompt Murdock to pull the plug. Certainly not money—who would have enough? But I think you may be on to something…