On the second anniversary of the bailouts of Fannie Mae and Freddie Mac, it's now obvious that weak lending standards, serving the political interest of affordable housing for all, were the main reason for the nation's mortgage meltdown. But the government just can't permit lending to anyone and everyone; it must insist on prudent judgment about who will repay and who will default. Not only will borrowers who lack a down payment, steady income, employment and a good credit history probably get into trouble -- surprise! -- but too much irresponsible lending also creates artificial demand for houses, driving prices into the stratosphere and, as we have just experienced, puts all homeowners at risk. The same mistake occurred in 1929, when any investor could buy stocks on margin with as little as 10 percent down. Small wonder that after the crash the government instituted a margin requirement of 50 percent down. Congress should apply the same principle to housing purchases, increasing the amount a buyer must put down and other safeguards to assure prudent lending. Congress refuses to do this. Why? Giving citizens cheap, easy housing is a great way to win votes, no matter what horrific repercussions ensue. Consider the prevailing narrative that holds a greed-driven private sector responsible for the 2008 financial crisis. A secondary narrative points to a greed-driven Fannie Mae and Freddie Mac abandoning their credit standards in an effort to follow the lead of Wall Street. If these explanations fail to convince, a third blames a combination of deregulation and insufficient regulation, again driven by greed, as rulemakers were asleep at their posts. What is missing is the central role played by an affordable housing policy built upon the misguided concept of loosened underwriting -- a policy created by Congress and implemented for 15 years by the Department of Housing and Urban Development and banking regulators. From 1993 onward, regulators worked with weakened lending policies as mandated by Congress. These policies systematically dismantled a housing-finance system based on the common sense principles of adequate down payments, good credit, and an ability to handle the mortgage debt. Substituted was a scam of liberalized lending standards that turned out to be no standards at all. In 1990, one in 200 home-purchase loans (all government insured) had a down payment of less than or equal to 3 percent. By 2003, one in seven home buyers had such a low down payment, and by 2006 about one in three put no money down. These policies led millions of Americans to buy homes with little or no money down, impaired credit and insufficient income. As a result, our economy has been brought down and the taxpayers have had to foot the bill for bailout after bailout. Congress and President Barack Obama's administration refuse to learn the lesson that is painfully aware to American taxpayers, and they have made it clear that they have no intention of fixing broken underwriting. The Dodd-Frank bill, signed in July 2010 by the president, omitted both an adequate down payment and a good credit history from the list of criteria indicating a lower risk of default as regulators sought to define a qualified residential mortgage. This was no oversight. Sen. Robert Corker, R-Tenn., and others proposed an amendment that would have added both a minimum down-payment requirement and consideration of credit history along with the establishment by regulators of a 'prudent underwriting' standard. This amendment was defeated. In early September 2010, Fannie and Freddie's regulator, the Federal Housing Finance Agency, following requirements set out in 2008 by Congress, finalized affordable housing mandates that are likely to prove more risky than those that led to Fannie and Freddie's taxpayer bailout. As required by Congress, these new goals almost exclusively relate to very low- and low- income borrowers. Meeting these goals will necessitate a return to dangerous minimal down-payment lending, along with other imprudent lending standards. As a society, we have to go back to at least 20 percent down, with limited exceptions. Credit histories need to be solid. Documentation has to be iron- clad. Lender capital levels need to be raised. Here's my proposal to bring Congress's penchant for imprudent lending to a quick end: All congressional pension assets should be invested in funds backed solely by the high- risk loans mandated by federal housing legislation. I have a feeling that things would change fast. 