Amanda Henneberg, a spokeswoman for the Romney campaign, said, "It is outrageous and offensive for President Obama to suggest that the majority of Americans who oppose Obamacare do not care about Americans suffering with serious, long-term medical conditions."
She said Romney believes his own plan would "replace Obamacare with patient-centered reforms, which include multiple elements to help those with pre-existing conditions, will better achieve the affordable access to high quality health care that the American people actually want."
As for Biden's remarks, the campaign also renewed its criticism of Obama for cutting projected Medicare spending by more than $700 billion as part of the health care law.
Romney spent Sunday at his Wolfeboro, N.H., vacation home, leaving only to attend church services with his wife, Ann.
Aides said he would spend much of the Democrats' convention week preparing for three fall debates with Obama, beginning on Oct. 3.
Running mate Paul Ryan was booked into North Carolina, counterprogramming the Democratic convention rhetoric.
Biden's appearance in Green Bay, Wis., was mostly devoted to domestic issues.
Earlier, campaigning in York, Pa., he took a swipe at Romney on foreign policy.
"He said it was a mistake to end the war in Iraq and bring all of our warriors home," the vice president said. "He said it was a mistake to set an end date for our warriors in Afghanistan and bring them home. He implies by the speech that he's ready to go to war in Syria and Iran. "
Democrats have been critical of Romney for making no mention of the war in Afghanistan when he accepted the Republican nomination in Tampa, Fla., last week. He previously criticized Obama for setting a public date for the withdrawal of U.S. combat troops from the war.
Romney also has faulted Obama for allowing the government of Syrian President Bashar Assad to remain in power. Yet his aides have refused to say for a week if he agrees with French President Hollande's promise to extend diplomatic recognition to a provisional government if Syrian rebels form one.
San Antonio Mayor Julian Castro delivers the keynote speech on Tuesday, followed by First lady Michelle Obama's remarks.
Obama and Biden will be nominated for second terms on Wednesday night, when former President Bill Clinton has the role of star speaker.
Biden and Obama, deliver their nomination acceptance speeches on Thursday, the convention's final night.
Ben Feller reported from Boulder, Colo. Associated Press writers Philip Elliott in York, Pa., Kasie Hunt in Wolfeboro, N.H., and Michael Biesecker, Mitch Weiss and Beth Fouhy in North Carolina contributed to this story.
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