SIOUX FALLS, S.D. (AP) — Republican presidential candidate Mitt Romney is telling a business group that the nation's economic challenges require a tested leader, as his campaign releases an Internet video that questions his top rival's readiness to be president.The former Massachusetts governor says America will overcome its problems "if we have leaders that...know how to lead."The 20-minute talk was upbeat and patriotic, a far cry from the GOP debate in Las Vegas Tuesday, where Romney and Texas Gov. Rick Perry tangled over policy and questioned each others' integrity.The Romney video knits together clips from recent debates where Perry jumbled his words and had trouble making his point.Romney was also raising money at an event hosted by a South Dakota meatpacking company owner. He'll campaign in Iowa Thursday.