US Republican nominee Mitt Romney has called for "real change" against President Barack Obama's "status quo", on the final stretch of an election race that is too close to call.
Mr Romney dismissed the Democratic incumbent as a shadow of his former self, in an economic speech in the key battleground state of Iowa.
On Friday, new figures showed US gross domestic product grew by 2% in the third quarter, exceeding expectations.
The US goes to the polls on 6 November.
Read more: BBC News