Qfyilyi

Dr. Michael Pillsbury, Senior Fellow and Director, Center for Chinese Strategy, testified before the US Senate (p. 9) on Nixon's visit to China:

But there were glimpses even then that the Chinese saw the United States not as an ally but as an obstacle. Referring to the United States, Zhou offered a hint of how the Chinese really felt about their new prospective friend. “America is the ba,” Zhou told Kissinger’s interpreter, Ambassador Ji Zhaozhu of China’s Foreign Ministry, repeating a term that would be frequently used by Chairman Mao and his successor, Deng Xiaoping.

[...] Kissinger’s translator told Kissinger that Zhou’s statement meant, “America is the leader.” This seemed to be an innocuous remark, and when taken in the context of the Cold War even a compliment. But that is not what the word ba means in Mandarin — at least that is not its full context.

How would that statement have been constructed in Chinese, and to which "ba" was being referred to?

I guess it was 霸 /ba4/ : tyrant; bully; overlord

Short for '霸主' (dominant leader among rulers) or '霸權' (dominant power)

It was not a friendly word toward America, because it implied America was a bully, (try to dominate other countries of the world with it's strength)

In ancient time, the difference between 霸主 (leader among rulers) and 天下共主 (common leader of the lords) is a 霸主 didn't have the loyalty of the other rulers. They submitted to him out of fear.

Since Zhou said "America is the ba" I presume he meant "America is the world's 霸主 (most dominant country)

Side note:

春秋五霸 were five rulers who earned the title of 霸主 during the warring state period.