Rolf Mowatt-Larssen, a professional expert on Soviet espionage techniques, has generously given us a peek into the world of Soviet espionage. He has described the purpose of Donnie's meeting with 2 Russian espionage assets and indicated that it went exactly as the Russian spymasters had hoped. That Donnie did not recognize this as an important meeting is hardly surprising.
The meeting was intended to feel out the Trump campaign and discover what Trump would do if the Russians ran their intended program of disruption and propaganda. The answer of course is that Trump would do nothing and did nothing in fact.
The question that needs to be asked now is, why did the Russians accept Donnie's indifference to their overture as permission to go full-speed ahead? Shouldn't they also be sure of Donald's response? Shouldn't the Russians ascertain whether Donnie told his father, Donald, about the meeting before they went ahead with their planned cyber attack? It seems to me they would want more assurance than the compliance of the candidate's son. Unless, of course, they had already gotten that assurance from Donald, something along the lines of, "Donnie speaks for me." But even then, they would want some assurance after the overture was made.
What if the Russians did receive such an assurance, in plain view, and the whole world heard it but didn't know what it meant?
Donald could have sent the ok to them in the form of a coded message, such as, "Why did Hillary erase 33,000 emails?" That would have fit into the cover story that Donnie told about what happened in the meeting, and it was a specific message the Russians would be sure to get but which would not obviously be an assent.
Everything Donald Trump and his associates did after this meeting is completely consistent with my assumption. Nothing that Donnie says about the meeting that cannot be independently verified makes any sense at all.