Barack Obama criticized likely general election rival John McCain on Wednesday where it could hurt most — the Arizona senator's reputation as a champion of ethics. Hillary Rodham Clinton, meanwhile, raised the possibility she might carry her fight to the Democratic convention floor.

Democratic presidential candidate Senator Barack Obama waves to the crowd with his wife Michelle after his speech at his Oregon and Kentucky primary election night rally in Des Moines, Iowa, May 20, 2008.

With more superdelegate endorsements after Kentucky and Oregon primaries the night before, Obama was just 64 delegates short of the 2,026 needed to clinch the nomination.

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.