Fear of communism made it more difficult for progressives to agitate for radical change. The prevailing atmosphere of Cold War paranoia meant that anyone vaguely left-of-center could find themselves tarred with the Communist brush. As numerous politicians and the public figures found to their cost, an accusation of Red sympathies, no matter how patently absurd, could be enough to destroy someone's career.
Anti-communist hysteria also undermined the rule of law. Millions of Americans—most of them not actually card-carrying Communists—found themselves harassed and persecuted by the authorities for their political beliefs, something that should never have been allowed to happen under the First Amendment.
Under the leadership of J. Edgar Hoover, the FBI played a leading role in rooting out alleged Communist subversion, often resorting to blatantly illegal methods such as unauthorized wiretaps. Hoover's work built on foundations that had already been laid during the previous Red Scare after World War One. But Hoover took anti-Communist persecution to a whole different level, greatly expanding the FBI's reach at the expense of individual liberty.
Finally, fear of Communism also led the United States to pursue a more aggressive foreign policy. A key component of this approach was the unswerving support—military, economic, and political—given to a variety of unsavory regimes across the developing world, who could be relied upon to counter the communist threat, often by the most brutal of methods. The Eisenhower Administration devoted huge resources, both financial and military, to propping up these client states as part of the world-wide struggle against the perceived communist menace.