That, in turn, could run into Romney's vow not to add to the deficit.
"My No. 1 principle is there'll be no tax cut that adds to the deficit," Romney said, in a clear break from longtime Republican orthodoxy that has held that tax cuts do not need to be offset.
Romney's statement appears to be an endorsement of the pay-as-you-go rules most Republicans have resisted for the past decade, a position that would presumably mean he'd have to block the small-business tax cut passed by House Republicans or the tax cuts proposed in vice presidential nominee Paul Ryan's own budget blueprint, for example. Neither would offset the tax breaks.
Obama has repeatedly violated pay-as-you-go budget rules and has added hundreds of billions of dollars to the deficit by passing various tax cuts, including much of his stimulus package and his payroll tax cuts. He has vowed to block any further extensions of the Bush-era tax cuts for people making more than $250,000, which would raise about $800 billion over the next decade, and he has enacted a number of other tax increases, particularly to help pay for his health care overhaul. Most of those tax increases, however, have not yet taken effect.
Obama has also proposed a much more modest plan to limit tax breaks - although not nearly to the extent Romney has - for only families making more than $250,000.
Romney noted, as he has previously, that you could eliminate various deductions instead of putting in a deduction cap, and he said he would work out the details with Congress.
"There are alternatives to accomplish the objective I have, which is to bring down rates, broaden the base, simplify the code and create incentives for growth," he said.
Rep. Bill Cassidy has his blood drawn by Alesha Barbour during a free hepatitis screening in the Rayburn House Office Building hosted by the Congressional Viral Hepatitis Caucus to recognize "National Viral Hepatitis Testing Day."
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