[159] Nixon announced the ground invasion of Cambodia on April 30, 1970, against North Vietnamese bases in the east of the country,[160] and further protests erupted against perceived expansion of the conflict, which resulted in Ohio National Guardsmen killing four unarmed students at Kent State University.[161] Nixon's responses to protesters included an impromptu, early morning meeting with them at the Lincoln Memorial on May 9, 1970.[162][163][164] Nixon's campaign promise to curb the war, contrasted with the escalated bombing, led to claims that Nixon had a "credibility gap" on the issue.[158] It is estimated that between 50,000 and 150,000 people were killed during the bombing of Cambodia between 1970 and 1973.[154]
In 1971, excerpts from the "Pentagon Papers", which had been leaked by Daniel Ellsberg, were published by The New York Times and The Washington Post. When news of the leak first appeared, Nixon was inclined to do nothing; the Papers, a history of United States' involvement in Vietnam, mostly concerned the lies of prior administrations and contained few real revelations. 