Task: Question Answering
Input (English): Passage: During the early part of the Second World War, Britain had a nuclear weapons project codenamed Tube Alloys. At the Quebec Conference in August 1943, the Prime Minister of the United Kingdom, Winston Churchill, and the President of the United States, Franklin Roosevelt, signed the Quebec Agreement, which merged Tube Alloys with the American Manhattan Project to create a combined British, American and Canadian project. The September 1944 Hyde Park Aide-Mémoire extended commercial and military cooperation into the post-war period. Many of Britain's top scientists participated in the Manhattan Project. The Quebec Agreement specified that nuclear weapons would not be used against another country without mutual consent. On 4 July 1945, Field Marshal Sir Henry Maitland Wilson agreed on Britain's behalf to the use of nuclear weapons against Japan.The British government considered nuclear technology to be a joint discovery, and trusted that America would continue to share it. On 16 November 1945, President Harry S. Truman and Prime Minister Clement Attlee signed a new agreement that replaced the Quebec Agreement's requirement for "mutual consent" before using nuclear weapons with one for "prior consultation", and there was to be "full and effective cooperation in the field of atomic energy", but this was only "in the field of basic scientific research". The United States Atomic Energy Act of 1946 (McMahon Act) ended technical cooperation. Its control of "restricted data" prevented US allies from receiving any information. Fearing a resurgence of American isolationism, and Britain losing its great power status, the UK government restarted its own development effort, now codenamed High Explosive Research.In 1949, the Americans offered to make atomic bombs in the US available for Britain to use if the British agreed to curtail their atomic bomb programme. This would have given Britain nuclear weapons much sooner than its own target date of late 1952. Only those bomb components required by war plans would be stored in the UK; the rest would be kept in the US and Canada. The offer was rejected by the British Chiefs of Staff on the grounds that it was not "compatible with our status as a first class power to depend on others for weapons of this supreme importance". As a counter-offer, they proposed limiting the British nuclear weapons programme in return for American bombs. The opposition of key American officials, including the United States Atomic Energy Commission's Lewis Strauss, and Senators Bourke B. Hickenlooper and Arthur Vandenberg, coupled with security concerns aroused by the 2 February 1950 arrest of the British physicist Klaus Fuchs as an atomic spy, resulted in the proposal being dropped. 
Question: What are the last names of the American senators that opposed the counter-offer to the offer rejected by British Chiefs of Staff?
Output (English): Hickenlooper.