I think this is a great line of attack to be honest, helps both to discredit the leaks and to build patriotic sympathy for the Clinton campaign.
right now this is mostly below the radar stuff, although I think Trump's campaign manager had to say something about this.
But could the message of how Trump is the favored candidate of Putin/The Kremlin be turned into 30sec TV ad without it looking like a kooky conspiracy theory?
It doesn't have to make it to an ad. Build it to a persistent background meme, and then attack him (say, during a debate) on something like the platform change, or refusal to support NATO. If he doesn't come back just right, then he's done - stake through the heart of his campaign right on the spot.
And Manafort
can't say anything about this. It'll only highlight his own ties to Viktor Yanukovych (and Putin), along with other shady characters - all of which will only make the allegations appear even truthier.
