President Barack Obama signed a memorandum on reducing student loan debt in 2014. A new estimate tries to pinpoint how much student lending could cost the government, not borrowers. It is an eye-popping number: $435 billion.  That is the amount of money the federal government can expect to lose on its $1.37 trillion student loan portfolio, according to an analysis consultants performed for the Department of Education. That analysis anticipates borrowers paying back $935 billion in principal and interest on their student loans, leaving $435 billion for taxpayers to absorb.