The question of what caused the crisis is obviously still controversial (though, Mr. Kessler notes, the official inquiry makes no mention of Mr. Bush's tax cuts). But a consensus seems to be forming around the following narrative: The federal government, out of an abundance of concern for the plight of the poor and middle class, made it too easy to buy a home. Congress, on a bipartisan basis, set unrealistic affordable-housing goals for Fannie Mae and Freddie Mac. President Bill Clinton used those goals to expand access to mortgages to low-income borrowers. Then President Bush, with the approval of Congress, expanded the practice, until way too many low-income or otherwise underqualified Americans owned mortgages they couldn't afford.