The quotation that will stick in the minds, and which will turn some undecided in favour of a Brexit, especially those over 50 years old, was "I think it's fair to say that maybe some point down the line there might be a UK-US trade agreement, but it's not going to happen any time soon because our focus is in negotiating with a big bloc—the European Union—to get a trade agreement done. And the UK is going to be at the back of the queue."
At about the same time he also tried to guilt trip the UK by mentioning World War 2 and the joint spilling of blood by UK and US forces.
I don’t think it was particularly smart of him to raise these two points together. Just for the record, here is an approximate, incomplete, and probably slightly inaccurate list of countries in the Second World War and the dates of joining. Note that the vast majority of allied countries, including most of Europe, only joined in after being attacked or invaded. This is the case with the USA. The UK and the Commonwealth were among those few allied countries joining the war without being attacked, on a matter of principle. (That the US used World War 2 as a business opportunity is perhaps worth a blog or two, but not by me.)
1 September 1939 Germany, Austria, Poland
3 September 1939 United Kingdom, Australia, New Zealand, Other Commonwealth countries including India, Ceylon, Burma, Rhodesia, Kenya, etc. France
Later in September 1939 Canada, South Africa, Nepal
April 1940 Norway, Denmark
May 1940 The Netherlands, Belgium, Luxembourg
June 1940 Italy
Oct 1940 Greece
April 1941 Yugoslavia
April 1941 Bulgaria, Hungary, Romania, Croatia, Iraq, Finland
June 1941 USSR, Mongolia
December 1941 Japan, USA (After Pearl Harbor), China, Korea
1942 Mexico, Brazil, Thailand
1945 Chile, Argentina
Back of the queue, huh? When it really matters, when national character is important, it’s not the UK that is back of the queue, Mr President. It is your own country. Shame on you for being so rude and ignorant.