“The Bush administration took a lot of pride that homeownership had reached historic highs,” Mr. Snow said in an interview. “But what we forgot in the process was that it has to be done in the context of people being able to afford their house. We now realize there was a high cost.” For much of the Bush presidency, the White House was preoccupied by terrorism and war; on the economic front, its pressing concerns were cutting taxes and privatizing Social Security. The housing market was a bright spot: ever-rising home values kept the economy humming, as owners drew down...