Did Communism pose a domestic threat to America?

Mostly exaggerated.

Explanation:

A study by the BDM Coporation asserts that the actual Soviet Threat was vastly over exaggerated by the U. S. The majority of the report comes from declassified NSA report released in 2009. To quote the report

"the defense industrial complex, not the Soviet high command, played a key role in driving the quantitative arms buildup" and thereby "led U. S. analysts to ... exaggerate the aggressive intentions of the Soviets"

There were of course monetary benifits to overstating the danger. Weapons, early warning systems, flash duck and cover films, sirens and so forth all bought at great expense. Another part of the report states;

"The Soviet military high command understood the devestating consequences of nuclear war and believed that nuclear weapons use had to be avoided at all costs."

It is possible to dismiss the report or slander it as revisionist propoganda, but the truth is that new finds and uncovered documents constantly update our view of history.