For various reasons, nearly all of them bad, the US clung to its alliance with the Pakistani generals despite repeated demonstrations that they were unreliable and frequently treacherous allies. This was much more dramatic during the Eisenhower and Nixon years than during the Kennedy administration, mostly because Nixon, like Dulles and Kissinger saw the world thru Manichean glasses. Relatively stable and progressive India, by pursuing socialist ideas and hewing to a neutralist line in the cold war became a "Soviet stooge" for them. Meanwhile, the repressive and incompetent but Sandhurst educated Pakistani generals spoke a language that they could appreciate, even when their double dealings were repeatedly exposed. In their conversations (as revealed by Nixon's tapes) Indira Gandhi was dismissed as a "bitch" and an "old witch".
Nixon did have one relatively good reason for hanging onto the Pakistani generals: Yahya Khan was his pipeline to the Chinese leadership and a key element in his plan to open relations with China.
Meanwhile Pakistan was falling apart. The Bengalis of East Pakistan, a badly treated majority in their own country, were sick of ill-treatment by the Pashtun and Punjabis of West Pakistan who dominated the military and government. After an election dominated by the Bengali party, Pakistan's generals plotted to hold on to power by military force.
The December 1970 election had brought Pakistan’s fissures to the fore. In response, West Pakistanis reacted with shades of ethnic superiority. Soon after the elections a general visiting Dhaka told his military colleagues: “Don’t worry. We will not allow these black bastards to rule over us,” a reference to the darker skin color of Bengalis compared to Pashtuns and Punjabis. 48 “The Punjab is finished, smashed,” an industrialist told the Times. “Our country has gone to the dogs,” he said, because “We will be ruled by Sindh and Bengal,” a reference to the fact that Mujib was Bengali whereas Bhutto was an ethnic Sindhi.
Haqqani, Husain (2013-11-05). Magnificent Delusions: Pakistan, the United States, and an Epic History of Misunderstanding (p. 150). PublicAffairs. Kindle Edition.
After feigning negotiations, Yahya Khan unleashed military repression.
US officials knew Ahsan and Yaqub [Pakistani officers who opposed the intervention] well, so Washington should have heard their views. But the United States chose to stand by Yahya. A new military commander, Lieutenant General Tikka Khan, arrived in Dhaka in March 1971 to enforce national unity with US weapons supplied ostensibly to save South Asia from communism. Pakistani soldiers then confined foreign journalists to their hotels before starting “Operation Searchlight,” a ferocious military action aimed at arresting and killing Awami League leaders. During this military operation at least ten thousand civilians were massacred within three days. There was a large Pakistani force already stationed in East Pakistan, but reinforcements and equipment were flown in from West Pakistan to bolster their strength.
Haqqani, Husain (2013-11-05). Magnificent Delusions: Pakistan, the United States, and an Epic History of Misunderstanding (p. 151). PublicAffairs. Kindle Edition.
US diplomats, the press, and much of Congress were outraged by Pakistan's atrocities, but Nixon and Kissinger were unwilling to risk their pipeline to China, even while they concluded that Yahya Khan was delusional and not very bright. Kissinger and Nixon may have brighter, but they were also delusional, attributing the slaughter in East Pakistan to Hindu-Muslim conflicts while in fact they were nearly completely irrelevant.
Nixon continued his delusional support of Yahya Khan even after India intervened on behalf of the Bengalis. The Pakistani army quickly collapsed and surrendered, but the generals continued their policy of attempting to deceive their own people.
The headline of Dawn, Pakistan’s major English newspaper, on the day of Pakistan’s surrender read, “Victory on All Fronts.”
Haqqani, Husain (2013-11-05). Magnificent Delusions: Pakistan, the United States, and an Epic History of Misunderstanding (p. 169). PublicAffairs. Kindle Edition.
Readers inclined to think of Kissinger and Nixon as both immoral and not too bright probably won't change their mind on the basis of Haqqani's book. The picture painted of Pakistan's military leadership is more like tragic-comically stupid.