Barack Obama came clean Sunday on his true motivation behind running for president — to keep his daughters safe from undesirable suitors.

"The real reason is Secret Service protection for my two girls as they enter into their teenaged years," the Democrat said, joking with voters at a barbecue in a woodland setting beside a lake.

"Whatever young guy comes by for a date, we're going to have one of these mean-looking guys who don't crack a smile. They're armed. They're dangerous," he said, pointing to the dark-suited agents monitoring the good-natured crowd.

Obama offered Secret Service vetting to a local man, so that he could investigate the background of his daughter's fiancé ahead of their wedding.

The Illinois senator has two daughters, Malia (10), and Sasha, who is seven. The girls will join their mother Michelle Obama at the Democratic nominating convention in Denver from Monday.

AFP