This claim struck me as especially dumb. We can easily determine whether or not he was a Russian asset by asking the question "Why is he in Russia?" He is in Russia because the U.S. cancelled his passport after he left China and before he got to Ecuador. He hasn't been able to leave because the U.S. won't restore his passport. And he's still on a temporary Russian visa. And even if he found a way to fly, the last time the United States thought (incorrectly) he was on a plane, they forced the plane (which was registered as a diplomatic flight) to land.

The conspiracy that he was flipped by Russia after he got there is at least not contradicted by the obvious facts, but a claim that he was a Russian agent all along is asinine.