By the end of the year, Khánh had prevailed in the power struggle with Khiêm and Minh. He despatched Khiêm to Washington as ambassador, being convinced Khiêm was destabilizing Saigon. In late December 1964, Khánh summoned Thảo back to Saigon. Thảo suspected Khánh was attempting to have him killed, while Khánh thought that Thảo and Khiêm were plotting against him. Fearing that he would be arrested upon arrival, Thảo attempted to outmanoeuvre Khánh and went underground to plot. In the meantime, Khiêm had been putting pressure on Khánh while serving as his ambassador by charging he and the Buddhists with seeking a "neutralist solution" and "negotiating with the communists". In January 1965, the junta-appointed Prime Minister
Trần Văn Hương introduced a series of measures to expand the military and war effort by widening the terms of conscription. This provoked widespread anti-Hương demonstrations and riots across the country, mainly from conscription-aged students and pro-negotiations Buddhists. Reliant on Buddhist support, Khánh decided to have the armed forces take over. On 27 January, he removed Hương in a bloodless coup. Khánh's deposal of Hương nullified a counter-plot involving Hương that had developed during the civil disorders. In an attempt to pre-empt his deposal, Hương had backed a plot led by some Đại Việt-oriented Catholic officers, including Thiệu and
Nguyễn Hữu Có. They planned to remove Khánh and bring Khiêm back from
Washington, D.C. The US Embassy in Saigon was privately supportive of the aim, By this time the US relationship with Khánh had broken down and the US became more intent on a regime change as Khánh was reliant on Buddhist support, which they saw as an obstacle to an expansion of the war. In the first week of February, Taylor told the leading officers that the US was not supporting Khánh, and they thought that Khiêm was a possible replacement although not among the most preferable. On 19 February, Thảo and General
Lâm Văn Phát began their coup attempt, seizing the military headquarters, the post office and radio station. Thảo made a radio announcement stating that he would remove the "dictator" Khánh, and would recall Khiêm to Saigon to lead the junta. Thảo had planned for Đôn to become Defense Minister and Chief of Staff of the military, but the Dai Việt insisted on installing the Catholic Khiêm. By this time, Khiêm was preparing to return to Saigon to join in on the action or take over if it became successful. His colleagues had anticipated that the Americans would give them an aircraft so that Khiêm could return to Vietnam, but second thoughts arose among Taylor and Westmoreland. The two American generals had lost confidence in Khánh, but the pro-Diêm political ideology being expressed by Thảo's supporters on radio alienated them, as they feared that the coup plotters would destabilize and polarize the country if they took power. The US wanted Khánh out, but were worried that Phát and Thảo could galvanize support for the beleaguered Khánh through their extremely divisive pro-Diêm views, which had the potential to provoke large-scale sectarian divisions in South Vietnam. The
Marine Brigade commander, General
Lê Nguyên Khang, appealed to the US Embassy in Saigon to not allow Khiêm to depart the US. As a result of this, Taylor messaged the State Department that "Regardless what ultimate outcome may be we feel Khiêm's arrival here ... would only add tinder to what this evening appears to be very explosive situation with possibilities of internecine strife between armed forces units ... Urge he not try return [to] Saigon until situation more clarified." Although the coup failed and Khiêm did not return, the Armed Forces Council adopted a vote of
no confidence in Khánh and
Nguyễn Cao Kỳ, and Thi became the most powerful figure in the junta. In the meantime, Thảo and Phát were sentenced to death in absentia. Thao was hunted down and killed in mysterious circumstances by other factions with the military leadership, while Phát evaded capture for a few years before surrendering and receiving a pardon from Thiệu. Despite his failure to take power, Khiêm said he was "very happy. I think my objective has been realized." The new junta decided to ignore Khiêm's involvement in the coup and he remained in Washington as the ambassador, with no further action taken. In October 1965 the junta of Kỳ and Thiệu made Khiêm the Ambassador to
Taiwan; he served there until mid-1968, then returned to Vietnam and served under President Thiệu as Interior Minister for a year before becoming Deputy Prime Minister at the start of 1969. In September 1969 he became prime minister and defense minister, Khiem lived in retirement in
San Jose, California, and was baptized as a Catholic there in 2018. He died on 23 or 24 June 2021, at the age of 95, while recovering from a fall at a nursing home around
Irvine, California. == Other awards ==