COUNCIL BLUFFS, Iowa – Led by President Barack Obama, Democrats claimed on Monday that Republican challenger Mitt Romney privately backs controversial plans to overhaul Medicare and cut trillions from social programs that his new vice presidential running mate has publicly proposed.

Rep. Paul Ryan "has given definition to the vague commitments that Romney has been making," Vice President Joe Biden said as the Democrats welcomed the Wisconsin lawmaker to the race with a barrage of criticism. "There is no distinction" between the two, he said.

Romney lauded his running mate's work as he resumed his own four-day bus trip through campaign battleground states.