Both the United States and the Soviet Union poured money into this election through their intelligence agencies and other sources, with the former attempting to sabotage Allende, and the latter supporting his campaign.

Eduardo Frei Montalva and his Christian Democratic Party would later unite with Allende's opponents to form a congressional majority in an attempt to declare his presidency illegal in August 1973, catalyzing the military coup a few weeks later.

[4][5] He spent a large portion of his political career campaigning for a coalition between Christian Democrats and Leftists, despite most of both groups consistently not supporting his idea.

However, it was hurt by his continued insistence on forming a coalition, as well as directly criticizing and attacking the Christian Democratic Party's own bills and the Frei administration's reforms.

[4][5] Voters often turned away from him due to his confusing campaign platform coming off as a more convoluted way of implementing socialism compared to instead electing Marxist Allende.

[4][5] Prior to running in the 1970 election, Jorge Alessandri was a career politician and served as the 27th president of Chile from 1958 to 1964, until the constitution barred him from succeeding himself.

At the time of the 1970 election, Alessandri was 74 years old and had experienced a variety of health issues, mental and physical,[5] including on national TV.

[7] Another major factor was his campaign being staffed mostly by amateurs, which led to the wasting of resources, creating of ineffective propaganda, issues mobilizing supporters, and trouble spreading a positive message to voters.

[9] In fact that represented only about half the money spent by the CIA to influence the election; the Church Committee put the total amount at between $800,000 and $1 million.

[10] The money approved by the 40 Committee was used in a "scare campaign" of posters and pamphlets linking an Allende victory with the violence and repression associated with the Soviet Union.

[8] Editorials and news stories reinforcing this message were also written with CIA guidance, especially in the newspaper El Mercurio, and disseminated throughout the national media.

After the elections, the KGB director Yuri Andropov obtained permission for additional money and other resources from the Central Committee of the CPSU to ensure Allende victory in Congress.

In his request on 24 October, he stated that KGB "will carry out measures designed to promote the consolidation of Allende's victory and his election to the post of President of the country".

During the elections he spent time analyzing each candidate and their campaigns, and would report back to the state department, making recommendations on how to handle involvement.

However, in this case, there was an active campaign against Allende's confirmation by Congress, including an intensified propaganda effort by the CIA to raise concerns about Chile's future.

[15] In the summer before the election, reports indicated that out of the 200 senators and deputies in Congress, Allende had 82 supporters, including the 80 members of Popular Unity,[2] a major organizing force in the coalition.

[16] Schneider was known for defending the "constitutionalist" doctrine, which held that the army's role is exclusively professional and aimed at protecting the country's sovereignty, not interfering in politics.

On 26 October, President Eduardo Frei appointed General Carlos Prats as the new commander in chief of the army, succeeding René Schneider.