I don't think its outlandish to believe Trump - a man notorious for surrounding himself with gadflies and sycophants - would suck up some FSB assets while populating his administration. And a personal meeting with the Russian President would be the perfect opportunity for an intelligence hand-off.

"Donald Trump wrote a list of CIA agents on his arm with a sharpie and showed it to Putin at the meeting" is goofy bullshit. But "someone in Trump's administration used their proximity to the President to harvest names from unredacted reports and feed them to the Kremlin in exchange for cash/favors/blackmail" is very easy to believe.

Hell, its not too difficult to believe moles existed in Obama, Bush, and Clinton administrations, either (or that the CIA has moles in the Kremlin). These are two of the most sophisticated and well-financed intelligence networks in the world. And guys like Yeltsin and Trump were both gullible rubes with deep mob connections who would be prime targets for this kind of infiltration.