“Oswald spent some time in Russia. He may have been given the mission there.”
From what I’ve read, the Russians didn’t give two craps about Oswald. Generally speaking, they had too many problems of their own to worry about taking care of foolishly idealistic American expatriates. I seem to recall Oswald attempting suicide so he wouldn’t be thrown out. The same goes for Cuba. Those guys wouldn’t even let him in the country.
Now, none of that means they didn’t use Oswald for their own purposes. All the bureaucratic red tape Oswald encountered trying to become a happy communist citizen could have all been a ruse. But why bother employing Oswald to shoot Kennedy? What was there to gain? What assurance did they have that Johnson would be better? What assurance did they have that their complicity wouldn’t be found out?
Sure, that's the official line. Would you have expected them to praise him openly before sending him back here to perform a 'hit' on an American president? (assuming of course they were behind it) They would want to distance themselves from him, at least publicly.