GOLDEN, Colo. (AP) — Mitt Romney promised Thursday that his economic program will create 12 million new jobs in the next four years, and likened President Barack Obama to a "dog trying to chase its tail" when it comes to strengthening the sluggish recovery.

Firing back instantly, Obama said his rival favors "trickle-down fairy dust" that has failed to fix the economy in the past, and unleashed a new television ad with a scathing summation of Romney's tax plans: "He pays less. You pay more."

The two men campaigned in battleground states hundreds of miles apart, the incumbent in Florida, his challenger in Colorado, both on a mission to convert undecided voters to their side in a race dominated by the economy and high joblessness.