A rare look inside Obama's campaign headquarters

President Obama's campaign for re-election later this year is set to be the most sophisticated ever seen in its use of technology and the internet.

His victory four years ago was seen by some a triumph of social networking techniques but this year's approach will be on much bigger scale in the battle against the Republican Mitt Romney.

The BBC's North America editor Mark Mardell has been given rare access to the Obama campaign headquarters in Chicago.