This is how.
In 1968, Moscow was so anxious to prevent the election of the veteran anti-Communist Richard Nixon that it secretly offered to subsidise the campaign of his unsuccessful Democratic opponent, Hubert Humphrey. Presumably much to Moscow’s relief, once in office, Nixon proved to favour détente with the Soviet Union. By the late 1970s, however, there was one US politician who, more than any other in the Cold War, caused fear and loathing in Moscow: Ronald Reagan.
During his unsuccessful bid for the Republican nomination in 1976, the KGB undertook a wide-ranging quest for compromising material on Reagan. It does not appear that the KGB’s investigations, for example into the alcoholism of Reagan’s father, had any effect on his failure to obtain the nomination that year. It did, however, plant some anti-Reagan articles in the foreign press outside the US. The KGB was less involved in trying to influence next presidential election, in 1980, than it had been four years earlier. This was because Moscow saw little to differentiate Jimmy Carter’s administration— dominated by the hard-line policies of his National Security Adviser, the Polish-born Zbigniew Brzezinski—from Reagan’s long-standing anti-Sovietism.
Moscow’s view dramatically changed with the prospect of Reagan serving a second term. The KGB’s Moscow headquarters (called the “Centre”) regarded it as an extreme priority to discredit the policies of his administration. It was probably this priority that led the Chairman of the KGB, Yuri Andropov, in one of the last acts of his 14 year leadership of the KGB, to decree in April 1982 that it was the duty of all KGB foreign intelligence officers, whatever their department, to participate in active measures.
In February 1983, the KGB instructed its main residencies (stations) in America to begin planning active measures to ensure Reagan’s defeat in November 1984. They were ordered to acquire contacts on the staffs of all possible presidential candidates, in both Democratic and Republican headquarters, making clear that any candidate, of either party, would be preferable to Reagan. KGB stations around the world were ordered to popularise the slogan “Reagan Means War.” The Centre announced five active measures “theses” to be used to discredit Reagan’s foreign policy: his militant adventurism; his personal responsibility for accelerating the arms race; his support for repressive regimes around the world; his attempts to crush national liberation movements; and his responsibility for tension with his NATO allies. Despite its best efforts, the KGB’s efforts to interfere with the election had minimal effect. Reagan won in a landslide.