CHARLOTTE, N.C. (AP) - While Democracts rally support for President Barack Obama at their national convention, Republicans continue to hammer away at the state of the U.S. economy under Obama's leadership.

Mitt Romney sent an email to his supporters saying that "no president in modern history has ever asked to be re-elected with this many Americans out of work."

Romney's running mate is portraying America as "a country in decline" because of the national debt piling up under Obama's watch. Campaigning in Iowa today, Paul Ryan noted that the national debt surpassed $16 trillion this week. He blamed Obama for "a gusher of spending."

Bill Clinton, the last president to preside over sustained economic growth, takes the stage tonight at the convention. Democrats are counting on Clinton's popularity to give Obama a boost. But former Republican New Hampshire Gov. John Sununu says Clinton's speech could "induce nostalgia for the days of balanced budgets and bipartisan accomplishments."

Obama addresses the convention tomorrow night. With a chance of thunderstorms in the forecast, officials have scrapped plans for an outdoor speech in a football stadium. Instead, Obama will speak to a smaller crowd in the arena where the rest of the convention events are taking place.

Copyright 2013 Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.