He led his forces into the mountainous areas of the Central Highlands to flush out pockets of Việt Cộng resistance and to prevent further infiltration from North Vietnam.

He often came into dispute with Diệm's brother, Ngô Đình Cẩn, who had his own autonomous private army and secret police and ruled the northern border regions of South Vietnam arbitrarily.

At the time, South Vietnam was gripped by widespread civil unrest due to Diem's suppression of the Buddhist majority, which responded with mass protests.

[2] Đôn claimed communists had infiltrated the monks at Xá Lợi and warned that ARVN morale was deteriorating because of the civil unrest and consequent disruption of the war effort.

[3][4] Hearing this, Diệm agreed to declare martial law effective on the next day, without consulting his cabinet, and troops were ordered into Saigon to occupy strategic points.

Don was appointed as the acting Chief of the Armed Forces in place of General Lê Văn Tỵ,[3][4] who was terminally ill with cancer and receiving medical treatment abroad.

[3][4] The real purpose of Đôn asking for martial law was to maneuver troops in readiness for a coup, and he had no concrete plans to send the regular army into the pagodas.

[8] In the wake of the raids, Đôn attempted to win over General Tôn Thất Đính, the commander of the forces which surrounded Saigon, so that he could encircle Diệm.

Đính, who was regarded as being vain, was reveling after having taken credit for the Pagoda raids, even though they were performed by the Special Forces of Colonel Lê Quang Tung.

At 10:00 on 1 November,[9] US Ambassador Henry Cabot Lodge Jr., General Paul Harkins and Admiral Harry D. Felt, the commander of US forces in the Pacific region, were invited to Gia Long Palace by Diệm.

Felt had been told of the existence of coup plans by Lodge, who falsely informed him that it was not imminent, saying "There isn't a Vietnamese general with hair enough on his chest to make it go.

[15] At 13:00, the plotters summoned many senior officers who were not involved in the plot to the Joint General Staff headquarters at Tân Sơn Nhứt Air Base, on the pretext of a routine lunchtime leadership meeting.

A civilian government and cabinet led by Prime Minister Nguyễn Ngọc Thơ was appointed by the MRC to ease some of the workload on non-military matters.

[26] A group of officers, led by Generals Nguyen Khanh, Tran Thien Khiem and Do Mau were unhappy with their posts after the 1963 coup, and began plotting.

Incriminating documents were concocted to purportedly show that Generals Minh, Kim and Đôn had been bought by French agents and were on the brink of declaring South Vietnam's neutrality and signing a peace deal to end the war with the North.

[27] Khánh told various American officials that Đôn, Kim and General Mai Hữu Xuân, along with Minh, were "pro-French and pro-neutralist" and part of French President Charles de Gaulle's plan to neutralise Vietnam.

[28] Lodge passed a report to Washington on January 20, alleging that Đôn and Đính were potential leaders of a group that might go along with de Gaulle's neutralization plan.

"[30] On January 30, Khánh launched a coup, arresting Minh, Dinh, Đôn and Kim, claiming that they were part of a neutralist plot with the Việt Cộng and taken to Đà Lạt.

[32] The day after coming to power, Khánh further claimed to Lodge that Đôn was in possession of briefing papers from the Americans on plans for the bombing of North Vietnam and said that they were in danger of being handed over to the communists.

[32] Worried that the group of idle officers would plot against him, Khánh made some preliminary arrangements to send them to the United States for military study, but this fell through.

[33] In September, Khanh survived a coup attempt by Generals Duong Van Duc and Lam Van Phat after the intervention of the 'Young Turks' faction of Nguyen Chanh Thi and Air Force chief Nguyen Cao Ky. To try and counter-act the increasing power of the latter, on November 14, Khánh brought back Don as the deputy chief of staff.

[39] The Young Turks then decided to try and sideline Don and the Da Lat generals by introducing a policy to forcibly retire officers with more than 25 years of service, as they thought them to be lethargic and ineffective, but most importantly, rivals for power.

[40] However, a civilian advisory body named the High National Council, composed mostly of old men, disagreed with this policy, and after refusing to approve it, the Young Turks launched a coup in December 1964 to remove the HNC.

[41] In February 1965, Don was again in view as Phat and Colonel Pham Ngoc Thao made another attempt to overthrow Khanh with the support of Catholic elements aligned with the Dai Viet Quoc Dan Dang and Diemist sympathisers.

[42] Eight months after the coup was over, Đôn told the American historian George McTurnan Kahin that he had been plotting with Thảo, who had planned for him to become Defense Minister and Chief of Staff of the military, but said the Dai Viet had insisted on installing the Catholic Khiêm.