Trump fires back: Mitt Romney 'would have dropped to his knees' for me in 2012
Donald Trump (Screenshot)

Republican presidential front-runner Donald Trump responded to Mitt Romney at an event in Portland, Maine on Thursday.

Romney, the Republican's 2012 presidential nominee, had attacked Trump earlier in the day, calling him a "fraud" who was "playing the members of the American public for suckers."

But the outspoken New York billionaire said Romney "begged" for his endorsement in 2012

"I don't know what happened to him," Trump said. "You can see how loyal he is. He was begging for my endorsement. I could have said Mitt 'drop to your knees.' He would have dropped to his knees."

Trump also described Romney as a "failed candidate."

Watch video, uploaded to YouTube by FOX 10 Phoenix, below: