"I do know that he never took on his party on any major issue," McCain said, appearing on CBS News' Face The Nation. "From the time he came up in the Chicago political arena to the time, the short time he was in the Senate, he never took on his party on a single major issue."
In contrast, the Republican Senator said he'd taken on his own party a lot.
In his acceptance speech at last week's Republican National Convention, McCain appeared to admit to his own party's failings, that even as Republicans were elected to the White House and Congress on a promise of changing government, "We let Washington change us."
"You even said, at one point, your party had lost its way," Bob Schieffer asked. "You said that Washington has to change and you're the one that can change it. But that's going to be a tall order, isn't it? Normally, it's the group that's out that says, 'Throw the bums out.' You're saying it was your party that was part of the problem and that you can be the agent of change.
"How do you convince people of that?"
"Well, Bob, I think we have to show them my record," McCain said. "I reached across the aisle to Democrats. And obviously I was very unpopular in some parts of my own party, whether it be on the issue of climate change or against Rumsfeld's strategy and the president's strategy in Iraq, or whether it be on campaign finance reform or a number of other issues that I fought against the, quote, 'special interests.'
"And the point is real - we now have former members of Congress residing in federal prison. So it was corruption. And I guess I'll say again what I said: We came to power to change Washington, and Washington changed us.
"But I have to make a strong case that we're going to bring about that change, and it's the right kind of change."
McCain was circumspect about some comments made by other speakers at the Convention (including former New York City Mayor Rudy Giuliani, former New York Governor George Pataki, and the vice presidential nominee Sarah Palin) who mocked Obama's post-collegiate work as a community organizer in Chicago, implying that it was a job without responsibility or value.
While saying he admired and respected all public service, McCain said the attacks were a response to criticisms by the Obama campaign that Palin's experience as a two-term mayor of a town of fewer than 6,000 people was insufficient for a VP nominee.
McCain called the questions about her experience "denigrating."
"I know that she shares my respect for all people, and appreciation for all people who serve their community and their nation," he said.
As for Obama's work aiding the disadvantaged, McCain said, "I do not think it's a negative. I think it's very honorable."
McCain also defended his pick of Governor Palin, whose speech at the convention appealed to the party's evangelical base but whose resume has been of concern even to some conservatives, with Charles Krauthammer of The Washington Post saying flatly "Palin is not ready" to become president and commander-in-chief at a moment's notice.
McCain pointed to Palin's popularity - "the most popular governor in America" - and said, without specifics, that she has a record of reform.
"She's not only talked about it, but she's done it, and she took on the people in her own party," he said. "She took on a sitting governor of her own party, and she reformed. And they passed ethics and lobbying reform. And she gave money back to the taxpayers and they cut spending.
"So in all due respect to any of the critics, what we want is the change in Washington. Who better in the political landscape could do that than Governor Sarah Palin, whose whole life has been engaged in that, taking them on and winning? I've taken them on and won less than she has.
"We've been campaigning together. The electricity has been incredible. And I would like to say it's all because of a charisma injection on the part of Mr. John McCain, but it's not - they're excited about this reformer, this lifetime member of the NRA, the person who was a point guard.
"I think that her experience and her background not only qualifies her, but brings to Washington a kind of an energy and a fresh wind that maybe is necessary in our nation's capital.
"I'm sure that Governor Palin has failings. And I'm sure she's made mistakes, because she's had a long career, from city council to mayor to governor. But the fact is, she's kind of what Americans have been looking for.
"And again, [with] all due respect to any critic, I think being mayor is a very important job nowadays, especially the way America is hurting."
On the economy, McCain said that help for small business (including tax relief) was important to "get this economy back on its feet.
"Americans are hurting in a way that they have not hurt for a long time," he told Schieffer, and said that on the 65 appearances the Senator had made on Face The Nation, "you and I have never had a conversation when our economy was in greater difficulty than it is today."
"You think it is?" Schieffer asked, "because you have said you think it's fundamentally sound"?
"Well, I have, because I have great confidence and faith in America, in our innovation and our capabilities," McCain said, "but these are tough times now."
Read the full "Face the Nation" transcript here.
By CBSNews.com producer David Morgan.