I think this is all a warning shot from the Russians. Trump had his meeting with Putin, and came away talking about the joint US/Russia cyber security initiative. Then grownups stepped in and he was forced to back away from it. As retaliation for that, and to remind Trump who he works for, the Russians prompted this information about Trump Jr.'s meeting to be released.
I think the Russians probably have a lot more things like this that they can reveal. Maybe even prostitutes peeing on hotel beds. It may not be worth what they think it is, though. Trump and 40% of the electorate seem to have a death grip on each other, regardless of everything.
