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Obama laughs off Trump's election vendetta

US President Barack Obama has an answer for why property tycoon Donald Trump keeps questioning his background.

"This all dates back to when we were growing up in Kenya," Obama said dryly to laughter from the audience at a taping last night of NBC's Tonight Show With Jay Leno.

Trump, who has previously questioned whether the president was born in the US and is eligible to hold the office, released a video on Twitter yesterday offering to donate $5m (¤3.8m) to the charity of the Obama's choice if he will release his college records and passport application.

Trump is backing Republican Mitt Romney in the presidential race.

Obama stopped in California to tape Leno's programme during a two-day trip to rally supporters before the November 6 election.

The host asked Obama why Trump seems to have a vendetta against him. Obama answered without missing a beat.

"We had constant run-ins on the soccer field," Obama, who was born in Hawaii, joked. "He wasn't very good and resented it. When we finally moved to America, I thought it would be over."