Any common ground they found on energy was lost in their divergent plan on health care. McCain called health care a "responsibility," while Obama called it a "right."
McCain wants to give families a $5,000 tax break that would allow them to look for affordable health care that best met their needs.
Obama, on the other hand, wants to continue with the current system, in which employees receive coverage through their jobs, but augment it with government funding to help the uninsured.
"If you've got health care already, and probably the majority of you do, then you can keep your plan if you're satisfied with it. We're going to work with your employer to lower the cost of your premiums by as much as $2,500 a year. If you don't have health insurance, you're going to be able to buy the same kind of insurance McCain and I enjoy as federal employees," Obama said.
Obama said McCain's plan would require taxes on the benefits workers receive from their employers and wipe out the ability of states to enforce regulations requiring certain tests, such as mammograms.
McCain said that Obama's plan would penalize small business owners and parents.
"If you're a small-business person and you don't insure your employees, he'll fine you," McCain said of Obama. "If you're a parent and you're struggling to get health care for your children, he'll fine you."
Down in the polls, McCain and his running mate, Alaska Gov. Sarah Palin, went on the offensive last weekend, aggressively attacking Obama for his association to 1960s radical William Ayers, a move some see as part of a last-ditch attempt to revive a flagging campaign.
McCain still has time and hopes that the attacks will swing the momentum in several important battleground states.
In Pennsylvania, Obama leads 48 to 38; and in Florida, 48 to 46, according to latest battleground polls monitored by ABC News' Polling Unit.
And a new ABC News/Washington Post poll indicates Obama has taken a commanding lead in Ohio, where days ago the two were virtually tied, in large part because of the area's economic difficulties.
Obama now leads McCain 51-45 percent among likely voters in Ohio, according to the poll.
Though 18 percent of the respondents said they had not yet made up their minds for sure, Obama had the advantage of the sheer energy of his backers: Fifty-eight percent of his Ohio supporters are "very enthusiastic" about his candidacy, compared with 30 percent of McCain's.