Both social security and medicare are legally obligated to be paid out. They are not even allowed to dip into general revenue; only their trust fund.
Oddly enough, Obamacare is what solvates medicare. Obama's 75 billion cut to medicare does a fairly good job balancing it out. Using Cox and Arnold's numbers (which are of course ridiculously overblown), the cuts amount to 57 trillion in liability savings.
Social Security is already solvent.
Plan for eliminating the national debt in 10-20 years:
Specific cuts; defense spending: http://rolexian.wordpress.com/2011/01/03/more-detailed-look-a