Eight years after arriving in Washington vowing to spread the dream of homeownership, Mr. Bush is leaving office, as he himself said recently, “faced with the prospect of a global meltdown” with roots in the housing sector he so ardently championed.

There are plenty of culprits, like lenders who peddled easy credit, consumers who took on mortgages they could not afford and Wall Street chieftains who loaded up on mortgage-backed securities without regard to the risk.

But the story of how we got here is partly one of Mr. Bush’s own making, according to a review of his tenure that included interviews with dozens of current and former administration officials.

From his earliest days in office, Mr. Bush paired his belief that Americans do best when they own their own home with his conviction that markets do best when let alone.