The Romney campaign hasn't spelled out what kind of tax deductions it wants to close in order to pay for lower headline income tax rates, but perhaps something related to horses could do the trick:
As millions tune into the Olympics in prime time this summer, just before Mr. Romney will be reintroducing himself to the nation at the Republican convention, viewers are likely to see “up close and personal” segments on NBC about the Romneys and dressage, a sport of six-figure horses and $1,000 saddles. The Romneys declared a loss of $77,000 on their 2010 tax returns for the share in the care and feeding of Rafalca, which Mrs. Romney owns with Mr. Ebeling’s wife, Amy, and a family friend, Beth Meyers.
It's of course true that curbing the deductibility of expenses related to the care and feeding of dressage horses might inhibit investment in the critical dressage sector of the economy. But I'm skeptical that incentivizing capital formation in this particular area is all that vital to the long-term prosperity of the country.
UPDATE: Some clarification here. The loss was over $77,000 but that only generated a $50 tax deduction. It's possible that the deduction will become much more valuable in the future if Rafalca generates fees.