Rowdy #GOPDebate audience boos Donald Trump during 'birther' attack on Ted Cruz

GOP front runner Donald Trump, who is an adamant birther, meaning he doesn't believe President Barack Obama is a U.S. citizen, has launched an attack against his closest rival, Texas Sen. Ted Cruz.

During the GOP primary debate on Thursday night, however, Cruz apparently came prepared to do battle. Trump and Cruz went head-to-head over whether Canadian-born Cruz, whose mother is a U.S. citizen, was qualified to be president.

The audience booed Trump as he pointed out that if he didn't raise the issue, the Democrats would do so. Trump hinted he would offer Cruz a position as vice presidential candidate if he was nominated. Cruz did the same for Trump. But Trump turned it down, saying he'd go back to real estate if he failed to secure the GOP nomination.

Trump admitted he raised the issue because Cruz is doing better in the polls.

Listen to the heated exchange, as posted to YouTube, here: