At a campaign rally in North Carolina, U.S. Vice President Joe Biden attacks Republican plans that he says would raise middle class taxes to fund tax cuts for the wealthy. (SOUNDBITE) (English) U.S. VICE PREIDENT JOE BIDEN: "How they can justify, how they can justify... raising taxes on the middle class that has been buried for the last four years? How in the Lord's name can they justify raising their taxes and these tax cuts?" In Iowa, Republican vice presidential candidate Paul Ryan hit back. (SOUNDBITE) (English) REPUBLICAN VICE PRESIDENTIAL CANDIDATE PAUL RYAN: "Vice President Biden just today said the middle class over the last four years has been 'buried'. We agree. That means we have to stop digging by electing Mitt Romney president of the United States." While the two camps sniped at each other from a distance, President Obama and Mitt Romney will be sparring face to face on Wednesday evening during a live TV debate in Denver. Romney took a break from preparation for the debate to visit a Mexican fast food chain. He is trailing Obama in the polls and on Tuesday softened his stance on immigration, in an apparent attempt to lure in Hispanic voters. President Obama meanwhile appeared relaxed as he visited the Hoover Dam. Obama will go into the debate appearing to have more momentum, despite high unemployment and criticism of his Middle East policy after the killing of the U.S. Ambassador to Libya.