On April 28 in Wilmington, North Carolina, he thought the month was "March" and that it was "nine months to November."
On May 13 in Cape Girardeau, Missouri, he claimed the war in Iraq was responsible for a shortage of interpreters in Afghanistan: "We only have a certain number of them and if they are all in Iraq, then it is harder for us to use them in Afghanistan." Iraqis speak Arabic or Kurdish. Afghans don't, speaking Pushtu, Dari, and various tribal languages.
On May 16 in a press conference, he claimed, "When Kennedy met Khrushchev, we were on the brink of nuclear war." The two met in Vienna in June, 1961. The Cuba Missile Crisis, which Obama claimed was resolved by the meeting, was in October 1962.
On May 18 in an interview to the Lexington (Ky) Herald-Leader, he said: "I'm not very well known" in Kentucky compared to Hillary because of her husband and "her coming from a nearby state of Arkansas." Illinois - the state he's a senator of - borders Kentucky; Arkansas does not (Tennessee's in between).
On May 9 in Beaverton, Oregon. You have to see it to believe he actually said that during his campaign, "I have now been to 57 states with one left to go," then says that one is "Alaska and Hawaii."
YouTube - Obama Claims He's Visited 57 States