After months of targeting US President Barack Obama, Republican presidential candidates are now taking aim at each other, just three weeks ahead of the Iowa caucus

After overtaking Mitt Romney as the frontrunner in recent polls, Newt Gingrich has become the most popular target for criticism by his opponents.

His critics point out he has paid an estimated $300,000 in fines for ethics violations and earned $1.5m in consulting fees from Freddie Mac - the US mortgage giant he now wants to abolish.

Al Jazeera's John Hendren reports from Washington.

Source: Al Jazeera