The Illinois senator confidently detoured from the three remaining Democratic primary states - Puerto Rico, Montana, South Dakota - to campaign in Florida, a crucial state in the November election. He also kept his focus on McCain, the Republicans' certain nominee in the fall.
Obama said the Arizona senator has lost faith with his own good-government principles.
Ten years ago, Obama said, McCain proposed barring registered lobbyists from working for candidates' campaigns.
"John McCain then would be pretty disappointed in John McCain now, because he hired some of the biggest lobbyists in Washington to run his campaign," Obama told a crowd of 15,000 at a Tampa arena.
McCain recently instituted a new no-lobbyist policy on his campaign, forcing out some top aides.
"And when he was called on it, his top lobbyist actually had the nerve to say the American people won't care about this," Obama said.
With McCain fundraising in California, campaign spokesman Tucker Bounds responded: "Despite his own rhetoric, Senator Obama still refuses to disclose the list of lobbyists advising his campaign.
What is Senator Obama hiding?"
"We challenge Senator Obama to meet our standard" for keeping lobbyists out of the campaign organization, Bounds added.
Clinton, too, was in Florida, pressing to narrow her gap with Obama by having delegates counted from its renegade January primary.
Democratic rule-makers are to meet May 31 to decide whether to count delegates from Florida and Michigan; the states were stripped of their delegates as punishment for holding early primaries in violation of party rules. Clinton won both states, but Obama had his name removed from Michigan's ballot and neither candidate campaigned in those states.
In an interview Wednesday with The Associated Press, Clinton said she is willing to take her fight to seat Florida's and Michigan's delegates to the convention if the two states want to go that far.
Asked whether she would support the states if they appeal an unfavorable rules committee decision to the convention floor, the former first lady replied: "Yes I will. I will, because I feel very strongly about this."
"I will consult with Floridians and the voters in Michigan because it's really their voices that are being ignored and their votes that are being discounted, and I'll support whatever the elected officials and the voters in those two states want to do."
Taking her battle to the convention would fly in the face of an increasing number of party leaders who say the contest needs to be wrapped up shortly after the last primary on June 3 to prepare adequately for the fall election.
Asked if she now envisioned the race extending beyond June 3, Clinton replied: "It could, I hope it doesn't. I hope it's resolved to everyone's satisfaction by that date, because that's what people are expecting, but we'll have to see what happens."
But trailing Obama by almost 200 delegates, even seating both Florida and Michigan delegations in the way most favorable to Clinton would still leave her behind the Illinois senator.
Clinton pressed this issue publicly at an appearance in Boca Raton in Palm Beach County, a key site in the battle between George W. Bush and Al Gore over the Florida presidential vote recount in 2000 that ultimately was decided by the Supreme Court.
Floridians "learned the hard way what happens when your votes aren't counted and the candidate with fewer votes is declared the winner," she told supporters. "The lesson of 2000 here in Florida is crystal clear: If any votes aren't counted, the will of the people isn't realized and our democracy is diminished."
"The people who voted did nothing wrong and it would be wrong to punish you," she added.
Obama wasn't asked about the delegate dispute at a town-hall meeting later in Kissimmee, but he did make a fleeting reference to his hope that Florida's delegation will be seated at the convention. He said nothing, however, about how the delegation's votes should be divided.
--- Associated Press writer Devlin Barrett in Boca Raton, Fla., contributed to this report.
