"I'd be willing to consider the president's plan, but he doesn't have one. That's right, in over three years he has failed to enact or even propose a serious plan to solve our entitlement crisis."
Instead, he said Obama "is the only president to ever cut $500 billion from Medicare. As a result, more than half of doctors say they will cut back on treating seniors.
The $500 billion cut was part of the health care law that Obama pushed through Congress, and the money would be used to help cover subsidies for those who can't afford the cost of insurance. Romney has pledged numerous times to seek the repeal of the health care law, but aides have said he would put the $500 billion toward deficit reduction, rather than restore it to Medicare.
David Axelrod, a top strategist for the president, said the budget Romney was defending would turn Medicare into a voucher program and that federal spending on education, research and development and renewable energy would take a "huge hit under their budget."
While Romney spoke to an audience of publishers and editors, Santorum insisted in his home state that he was forging ahead with his campaign.
"People in Pennsylvania know me. We've got a strong base of support here, and we're going to work very, very hard," he said, referring to the state's primary on April 24.
"Then we're going to get into May. There's movement in Texas to make Texas a winner-take-all state. You throw those 154 delegates on our ballot and all of a sudden this race becomes a very different race."
The Associated Press delegate count shows Romney with 658 delegates, more than halfway to the 1,144 needed for the nomination. Santorum has 281, Newt Gingrich 135 and Ron Paul 51.
The candidates face a three-week primary intermission before the next contests in Pennsylvania, New York, Delaware, Connecticut and Rhode Island.
Associated Press writers Kevin Begos in Pittsburgh and Ken Thomas in Washington contributed to this report.
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