[Gerald F. Seib writes for the Wall Street Journal.]

As a piece of social policy, the health bill passed Sunday night by the House of Representatives ranks up there with the Great Society programs of Lyndon B. Johnson in ambition and scope. But here's one big difference: The Great Society programs were enacted in an era when Americans still tended to trust the government to get things done.

By contrast, a principal reason the health bill was so hard to get to this point, and the reason it's such a political risk, is that this landmark legislation proposes expanding the government's role in the giant health economy at a time when Americans are far less likely to trust the government to do things right....

Proponents of the health legislation are quick to point out that it doesn't amount to a government takeover of health care, and they are right. The legislation builds on, rather than replaces, the employer-based health-insurance system that has prevailed in this country for decades. It funnels patients getting government subsidies into private insurance policies and pools, not a government-run health plan, and is at best a small step toward the nationalized health-care system some liberals want.

So in that sense, it's a far more modest exercise in social engineering than was the Great Society program of the mid-1960s, which included legislation creating Medicare and Medicaid, the food-stamp program and Head Start, as well as two landmark civil rights acts....

When President Johnson led the drive to create Medicare and Medicaid, Americans saw before them a government that had won World War II, built the interstate highway system and launched an almost universally admired space program that was headed toward putting a man on the moon. The New Deal was widely considered the reason the Great Depression finally was vanquished. "Liberal" was such a coveted label for a politician that one of President Johnson's deep worries when he took over after President John Kennedy's assassination was that he might be seen in Kennedy circles as too conservative.

Since then, attitudes have soured. The Vietnam War went from nuisance to debacle, tarnishing for a long while the notion that the nation's best and brightest minds were at work in Washington dealing brilliantly with difficult problems....

The result has been an erosion over time in confidence in government's competence. One of the best barometers of that shifting attitude is found in polling done by the Gallup organization, which for four decades has been testing Americans' trust in government. When Gallup asked in 1972 how much Americans trusted the federal government to handle domestic problems, 70% said they had a "great deal" or "fair amount" of trust. By last year, that had fallen to 51%—almost even with the 48% who said "not very much" trust, or "none at all."...