The time period from 1976-1980 was their last best shot at expanding communism.
Our military was weak and hollowed out after Vietnam. We had a feckless leader in the WH. Our European allies, save England, would have abandoned NATO.
I well remember the concern that the Ruskies were winning and we were losing.
When they invaded Afghanistan I thought it was a precursor to invading Iran.
Imagine the world scene if that'd happened!
In 1977 or so I had a SPI board game that posited an Socialist World Order invasion of the United States some time around the end of the century. In 1977, it was not a far-fetched idea.