钱学森诺贝尔奖的堂侄概括的基本正确，“他当时因为和共党有关，最后回中国了”。
1950年，钱学森被吊销了接触机密的安全许可。理由是他和当时美共活动在湾区的一个党支部有关联。FBI找到了一份名字是 H.S.Tsien 的党员登记表。有证人说和钱学森一起啃过恩格斯的“反杜宁论”。 另外钱学森1947年回国奔丧期间写给美国同事的信件，里面流露了钱学森对当时中国国民大会选出的合法政府的失望和不满。
钱学森的反应是预定了加拿大航空飞温哥华的机票，以及从加拿大到香港的船票。还请了搬家公司来打包。这个时候他犯了第一个错误。他同时决定去首都走走关系，看能不能重新拿回安全许可。据 “China Cloud“一书（BY WILLIAM RYAN and SAM SUMMERLIN， 1967），这一决定是加州理工校方的建议，钱学森 ”He did so, but with reluctance“。 钱学森要找的关系是Dan A. Kimball, then Under Secretary of the Navy。 不知道他这个官衔中文咋说。钱和他是老熟人了。
Kimball告诉钱学森，”我不相信你是共党“， 并答应尽力帮钱学森努力。但是钱学森犯了一个致命的错误，他透露了回国的打算。 原话是 ”I'm Chinese, I don't want to build weapons to kill my countrymen. It's that simple.“。 等钱学森一离开，Kimball立刻打电话给国务院，”Under no circumstances, should Tsien be permitted to leave the United States.“。 还有就是那句著名的 ”I'd rather shoot him than let him leave the country; he knows too much that's valuable to us; he's worth five divisions anywhere.“。
钱学森回家在洛杉矶机场知道了见Kimball的结果，移民局的官员向他传达了禁止离境的命令。 由搬家公司运往香港的总重1800磅的行李被由八家执法机构组成的联合调查组扣留。
1950年9月6日，钱学森在家中被逮捕。罪名是”a member of an organization ... that advises, advocates or teaches the overthrow by force of the Government of United States.“。 两星期后，以15000元取保候审，钱学森被释放回家。数周后，美国政府对钱学森一案开庭。下面就是那段庭上著名的问答
"Do you owe your allegiance to Communist China?"
"I do not," Tsien replied.
"To whom do you owe allegiance?"
"I owe allegiance to the people of China."
检察官 sparred with Tsien for a moment and then demanded: "In the event of a conflict between this country and Red China, would you fight against Red China for the United States?"
Tsien parried. The situation had not presented itself. There was no such war. Again, Tsien's lawyer protested. His client would need time to think about such a question.
"We will wait here six months," 检察官 snapped.
But Tsien volunteered that it would take only moments. The room fell silent. Five minutes ticked by. Finally, Tsien said, "I can't answer the question now."
"You can't or won't answer the question now?"
"I can -- c-a-n -- answer the question now," replied Tsien, stung, "and the answer is as follows: I have already said that my essential allegiance is to the people of China, and if the war between the United States and Communist China is for the good of the people of China, which I think is very likely to be, so then I will fight on the side of the United States. No question about that."
"But you will make the decision first? You will determine whether it is for the good of the Chinese people?".
"That decision, yes, I would make."
"You will not permit the Government of the United States to make that decision for you?"
"No, certainly not."
1951年4月26日裁定 “Tsien was an alien, a native and citizen of China, who was subject to deportation on the grounds that he has been found to have been, prior to entry ... an alien who was a member of the Communist Party of the United States.” 钱学森被判递解出境，但考虑到美国的国家安全，钱学森被禁止离开他当时居住的洛杉矶县（COUNTY）。
1955年司法部撤销了禁止钱学森外出的命令， 驱逐钱学森的判决立即生效。钱登上了开往香港的轮船。与此同时11名被扣押的美军飞行员跨过了罗湖桥进入香港。
"It would be totally contrary to our principles, The United States has not been engaged and is not now engaged in swapping human beings." 这是美国国务院对此事的正式答复。