In addition to the substantive objections that members of Congress may have to any kind of fiscal deal, you should never forget about the politics part of politics. Cutting Social Security benefits slightly is wildly popular with Pete Peterson, Pete Peterson's son, the Peter G. Peterson Foundation, and a broad array of groups funded in whole or in part by the Peter G. Peterson Foundation. But as today's Washington Post poll shows, it's broadly unpopular with the American people since as a pure cash transfer it's essentially a waste-free program and since retirement programs—unlike targeted programs from the poor—gain public support from white ethnocentrism rather than losing support.
Obviously any deal would be a bipartisan deal, but "bipartisan cover" isn't everything it used to be. Republicans and Democrats alike—including all the leaders of both parties—backed TARP in 2008, and pro-TARP Republicans and Democrats were both hit by their general election opponents in 2008 and 2010 for their trouble. A Republican who votes to cut Social Security benefits will be hit for cutting them in order to cut taxes on the rich, and a Democrat who votes to cut Social Security benefits will be hit for cutting them in order to finance a spending binge on lazy welfare moms.