Let's assume that:
Ronald Reagan is assassinated;
Pope John Paul II is assassinated and sufficient evidence of WarPac intelligence involvement in the conspiracy emerges;
by whatever political butterflies necessary within the Soviet Politburo (in all likelihood including the early death of Andropov, that opposed intervention IOTL), the USSR reacts to the rise of the Solidarnosc movement in Poland by invading the country in 1980-82 (anytime from late 1980 to early 1982, depending on butterflies).
The invasion ends being a rather bloody affair much akin to 1956 Hungary, with a sizable amount of Pole insurgents (quite possibly including sectors of the Polish army that side with the rebels) fighting the invasion for days or weeks (even if the Red Army is of course victorious in the end).