Sihanouk, having effectively destroyed the ability of the Democratic Party and the socialist
Pracheachon opposition to function, now made an attempt to co-opt young leftists into the Sangkum movement; amongst the prospective candidates Hou Yuon,
Chau Sau, Uch Ven and Hu Nim all won seats. Nim became Under-Secretary of State in the office of the
Prime Minister, and held a variety of junior ministerial posts over the next nine months. More significantly, he began to build up a substantial base of support in his Kampong Cham constituency, which he was to represent for the next nine years, becoming one of the most visible and well-known Cambodian leftists. By the early 1960s, Nim had joined the staff of the Sihanoukist daily newspaper
Neak Cheat Niyum, and after a trip to
Beijing was asked to form the
Khmer-Chinese Friendship Association; he also travelled to
Pyongyang and to
Hanoi, where he met
Ho Chi Minh. Continuing his studies in law at the
University of Phnom Penh, he completed his doctoral thesis, on land tenure and social structure, in 1965. The 1966 elections resulted in domination of the Sangkum by its rightist elements, though thanks to his local popularity, Hu Nim (along with Hou Yuon) was able to retain his seat, despite Sihanouk actively campaigning against him. He was briefly made part of a leftist "counter-government" set up by Sihanouk to balance
Lon Nol's right-wing cabinet, but from this point the political tide was to turn against the remaining leftists who had not already joined the Communist underground movement. The situation was inflamed in March–April 1967 by a revolt in the far north-east of the country, the
Samlaut Uprising, that was blamed by Sihanouk on left-wing agitation, and specifically, though most likely incorrectly, on the activities of the remaining openly leftist politicians: Hou Yuon,
Khieu Samphan,
Chau Seng and Hu Nim. The first two men, threatened with arrest, a military tribunal, and calls from right-wing members of the Assembly for their immediate execution, fled to join the Communist guerrillas in late April. Hu Nim was later to write that he initially joined them, but returned to the capital after a few days, having been persuaded by senior cadre
Vorn Vet that it might be profitable to continue engagement with Sihanouk and persist in anti-government agitation. Sihanouk, however, was to respond by calling Nim "dangerous", and to ban the Khmer-Chinese Friendship Association. An attempt by Nim to submit a petition for its reinstatement backfired dramatically, when it was discovered that the cadres who had collected the thumbprints used for signatures had done so under false pretences: Sihanouk called a meeting where he admonished Nim in person as "a little hypocrite" whose "words carry the scent of honey, but [who] hides his claws like a tiger", adding that he "had the face of a Vietnamese or Chinese". In this climate, it was unsurprising that Nim soon received instructions from Vorn Vet to take to the forests. On 5 October, Sihanouk warned him that he would be "subjected to the military tribunal and the execution block"; he left for the
Cardamom Mountains, escaping waiting intelligence agents, two days later. Like Hou Yuon and Khieu Samphan, Nim was widely assumed to have been murdered by Lon Nol's security police. ==The GRUNK==