Barack Obama and Mitt Romney clashed over taxes, healthcare and the economy at the University of Colorado in Denver, with Romney going first:

"Under the President's policies the middle-class Americans have been buried, they're just being crushed. Middle-income Americans have seen their income come down by 4300 dollars, this is a tax in and of itself. I'll call it "economy tax". It's been crushing. At the same time the gasoline prices have doubled under the President, electric rates are up, food prices are up, healthcare costs have gone up by 2500 dollars a family. Middle-income families have been crushed"

Obama retorted: "Four years ago when I stood on this stage, I said I would cut taxes for middle class families. And that's exactly what I did. We cut taxes for middle class families by about 3600 dollars. The fact is that if you're lowering the rates the way you describe, Governor, then it is not possible to come up with enough deductions and loopholes that only affect high-income individuals to avoid either to raise the deficit or burdening the middle class. It's math, it's arithmetic".

Polls suggest Obama is slightly ahead of Romney. But there is time yet.

The debate is the first of three scheduled over the next four weeks.