evidence: Washington was uncertain about how to follow up Seoul’s liberation but MacArthur was determined to march north to the Yalu River and the Chinese border. Mao, for his part, decided in early October to send his army south across the Yalu River and fight MacArthur’s forces. [...] MacArthur made one of his lightning quick trips to Korea from Tokyo on November 24, 1950, telling the U.S. ambassador in Seoul there were only 25,000 Chinese troops in Korea. Then he had his return flight to Tokyo fly along the Yalu River, making possible a personal reconnaissance intended to impress the media. His report to Washington dismissed the danger of Chinese intervention. Three days later Peng’s armies struck the American forces as they were driving to the Yalu River. [...] The catastrophe on the Yalu would have a lasting impact on American thinking about China for decades. Coming after the communists’ victory in the Chinese civil war, the Korean debacle fueled a domestic political debate over "who lost China" that pitted the handful of China experts in Washington against a powerful lobby that argued the China hands were either soft on communism or, worse, were communist agents serving foreign interests. Led by Senator Joe McCarthy and Congressman Richard Nixon, the right wing of the Republican Party fought any effort to rethink American policy toward China, to give the PRC the UN Security Council seat, or even to talk with China for the next two decades. Ironically it would be Nixon who finally implemented all of these changes in 1971.