Brzezinski himself. He has talked about it for years. He tried to couch the result, but the facts are the facts.
Here is a link to an interview from 1998: https://dgibbs.faculty.arizona.edu/brzezinski_interview
Excerpt:
B: It wasn’t quite like that. We didn’t push the Russians to intervene, but we knowingly increased the probability that they would.
Q : When the Soviets justified their intervention by asserting that they intended to fight against secret US involvement in Afghanistan , nobody believed them . However, there was an element of truth in this. You don’t regret any of this today?
B: Regret what? That secret operation was an excellent idea. It had the effect of drawing the Russians into the Afghan trap and you want me to regret it? The day that the Soviets officially crossed the border, I wrote to President Carter, essentially: “We now have the opportunity of giving to the USSR its Vietnam war." Indeed, for almost 10 years, Moscow had to carry on a war that was unsustainable for the regime , a conflict that bought about the demoralization and finally the breakup of the Soviet empire. ...
Thank you for the info, sounds like a successful operation then.