"I think it's very hard for Senator Clinton to break out of the politics of the past 15 years," Obama said.
"Senator Clinton starts off with 47 percent of the country against her," the Illinois senator told 3,000 people at a high school gym in Alexandria, Va., just outside Washington. "That's a hard place to start."
"Hillary and I both want universal health care," he said.
"But unless we can put a working majority together, it doesn't matter what plan is adopted" because Congress will not pass it.Virginia, Maryland and the District of Columbia hold Democratic primaries Tuesday.
Obama was buoyant after winning three more state contests Saturday, and Maine on Sunday, telling a crowd of 18,000 in Virginia Beach, Va. Sunday evening that "we have won on the Atlantic Coast, we have won on the Gulf Coast, we have won on the Pacific Coast" and places in between.
Taking audience questions earlier or the first time in several days, he used similar queries from two women to remind voters of the former first lady's ties to an administration and an era that many independents and Republicans remember with distaste.
"I have the ability to bring people together," he said. Because of that, he said, "I think I can beat John McCain more effectively," referring to the Arizona senator closing in on the Republican presidential nomination.
One woman told Obama that her 9-year-old son adores him, her husband was out campaigning for Clinton and she was undecided.
Obama posed for a photo with the boy as the crowd laughed and cheered. Then he gave a minute-long recitation of why his mother should choose him over Clinton.
Obama said he rejects federal lobbyists' money, unlike Clinton, and has been more forceful in supporting full disclosure of money's role in politics.
"Senator Clinton does not have that track record," he said.
He repeated a jibe at Clinton's comment from one of their debates, in which she said she voted for a bankruptcy bill but was glad it never became law.
"That kind of talk, I think, it makes people not trust government," Obama said.
He planned a rally in Virginia Beach, Va., on Sunday, and events in Roanoke, Va., Baltimore and College Park, Md., on Monday.
