After U.S. covert operations, which led to the assassination of Chilean Commander in Chief of the Armed forces General Rene Schneider, failed to stop Allende's inauguration on November 4, 1970, Kissinger lobbied President Nixon to reject the State Department's recommendation that the U.S. seek a modus vivendi with Allende. In an eight-page secret briefing paper that provided Kissinger's clearest rationale for regime change in Chile, he emphasized to Nixon that "the election of Allende as president of Chile poses for us one of the most serious challenges ever faced in this hemisphere" and "your decision as to what to do about it may be the most historic and difficult foreign affairs decision you will make this year." Not only were a billion dollars of U.S. investments at stake, Kissinger reported, but what he called "the insidious model effect" of his democratic election. There was no way for the U.S. to deny Allende's legitimacy, Kissinger noted, and if he succeeded in peacefully reallocating resources in Chile in a socialist direction, other countries might follow suit. "The example of a successful elected Marxist government in Chile would surely have an impact on — and even precedent value for — other parts of the world, especially in Italy; the imitative spread of similar phenomena elsewhere would in turn significantly affect the world balance and our own position in it."

The next day Nixon made it clear to the entire National Security Council that the policy would be to bring Allende down. "Our main concern," he stated, "is the prospect that he can consolidate himself and the picture projected to the world will be his success."

from the first link:

And on September 16, 1973, just six days after Pinochet’s bloody putsch, Nixon called his national security adviser to ask whether the US “hand” in the coup would show. According to declassified call transcripts, Kissinger admitted that “we helped them” and that “[deleted reference] created conditions as great as possible.”