A Framework for Assessing Potential Changes – GAO-15-131: Published: Oct 7, 2014. Publicly Released: Oct 7, 2014.

“Developments in the single-family housing finance market from 2000-2013 led to changes in the federal government’s role in the housing finance system and ultimately to a significant increase in that role. For example:

• Before the 2007-2009 financial crisis, the market share of nonprime mortgages—loans often made to borrowers with high-risk characteristics and funded by mortgage backed securities (MBS) issued by private institutions without a federal guarantee (private-label MBS)—grew but fell dramatically during the crisis.
• As this market segment grew the share of new mortgage originations (refinances and purchase loans) insured by federal entities—the Federal Housing Administration and the Departments of Veterans Affairs and Agriculture—fell from 11 percent in 2000 to less than 3 percent of the value of new originations in 2006 but, with the onset of the crisis, the market share of these mortgages rose as high as 25 percent before declining to 20 percent of the market in 2013.
• The market share of new mortgages backing MBS guaranteed by Fannie Mae and Freddie Mac (the enterprises) fell from 36 percent in 2000 to 27 percent in 2006 but stood at 61 percent in 2013.
• In 2008, when the enterprises’ weakened financial condition led to their being placed into conservatorship, the federal government’s support for them became explicit. 
• In 2013 the federal government was providing support either directly or indirectly for 81 percent of the value of all new mortgages. In addition, during the crisis, the Federal Reserve System and the Department of the Treasury began purchasing MBS issued by the enterprises. The Federal Reserve System began reducing these purchases in January 2014, and Treasury completed the sale of its MBS investments in fiscal year 2012.”