It began to sink into the political class last week that Barack Obama's push for health care reform could fail. If it does indeed fail, it would be a stunning knockdown blow to Obama's presidency. He would likely never be as powerful thereafter.

A president's bully pulpit is only as powerful as the perception of that power. The history framing Obama, from the first he embodies to the economic collapse, strengthened Obama early on. It also meant that his stature was fragile. His strength was rooted in hope, not accomplishment. And hope can quickly fade without success.

Health care reform represents Obama's first major legislative battle. Obama has already won a successful stimulus package. But he faced little real opposition. Health care reform will be far more difficult. And the president realizes it. This Wednesday Obama holds a one-hour "town hall" on his health care agenda, broadcast on ABC News from the White House.

A Democratic vision of success likely includes a government-backed health insurance program. Passage would leave Obama politically stronger. Over the long haul it would likely improve the public's perception of government, an existential interest of the political left. In the near term, a successful health care overall would offer momentum to other legislative efforts, from energy to immigration reform.

But the converse is no less true. It was four years ago that George W. Bush's effort to reform Social Security began to sink. That year he gave more speeches on Social Security than the Iraq war, all to no avail.

The bully was lost from Bush's pulpit. By cause or coincidence--certainly the war in Iraq was the greatest long-term albatross--it was at this point that Bush's approval rating began to slide from bobbing around 50 percent to the low 40s by autumn, and on downward.

But it's the lessons of Bill Clinton's failure that consume this White House. There is a tendency in Washington to overestimate the providence of a moment. And in 1993, there was a great deal of hyperbole about Clinton's moment. The Washington Post's David Broder offered a more sober voice. He wrote in September 1993 that Clinton's push for national health care represented the "most ambitious domestic undertaking by a chief executive in many a generation." Broder added that, "The financial, political and lobbying barriers are formidable."

Those barriers held. Clinton's failure was not the first, only the most damaging.

Health care reform trails back nearly a century. Teddy Roosevelt called for national health care in the 1912 campaign. By 1945 Harry Truman, in a special address to Congress, became the first sitting president to publicly push for a national health care program.

The opposition proved too strong for Truman. By 1961, a young Ronald Reagan, as advocate for the American Medical Association (AMA), recorded a roughly 10-minute record arguing that even the partial nationalization of health insurance was an "excuse" to implement "socialized medicine."

Today the AMA, like other powerful commercial interests, opposes a public option that competes with private insurers. And it’s possible real reform could depend on the outcome of this private-public debate.

The United States is the only industrialized nation without a universal health care system. Americans are not, on average however, healthier than citizens of most other wealthy nations.

There were some 37 million Americans without insurance when Clinton pushed for universal health care. That number has risen to 46 million today.

At least six presidents have sought some version of health care reform. But only Clinton made it his first major legislative effort. And he lacked the power of Obama. Clinton won with 43 percent of the vote, 10 percentage points less than Obama. He got sidetracked with the debate over gays in the military. And his staff went about reform badly. The overhaul was privately prepared. The bill came out of the White House and not Congress. Clinton did not strongly push for deadlines on the issue.

By contrast, Obama left the plan to Congress. He is pushing for legislation this summer. He also benefits from the ongoing nature of the health care debate over the past decade. Many incremental policy battles are fought and resolved. Obama is also, unlike Clinton, not governing in a conservative era. Events of the day, from this recession to issues abroad, also offer Obama moments to appear more presidential and therefore more powerful.

But it's also expensive. Last week a government estimate placed the tab at $1.6 trillion over 10 years. The cost caught Democrats off guard. Trimming and tailoring is underway. More problems are likely ahead.

The most successful active state presidents of the twentieth century never attempted heath care reform. Not Teddy or Franklin Roosevelt or Woodrow Wilson. Johnson vested early political capital into Medicare and Medicaid. But in time, Vietnam sunk the momentum of Johnson's domestic agenda.

This president is more prudent than gambler. He is not Johnson. He won't go all in. And yet he chose health care to make his first big fight. And Obama's later legislative ambitions now ride on his success.

Obama has already slipped with the public. His job approval rating, based on the RealClearPolitics average, is now below 60 percent. Any ebb in popularity makes legislative failure all the worse for Democrats.

Obama and Democrats have much to gain by significant reform. Therefore Republicans have much to win by a Democratic defeat on any bill of this magnitude. Obama's Democratic majority in Congress, like Clinton, makes success more possible. But it also adds more pressure. Failure would look like another Democratic president unable to corral his party. "That might make the fall that much more severe," as Columbia University political scientist Robert Shapiro put it.

And yet the potential fall means compromise is likely. This White House wants some bill to be law. The outcome may be more painkiller than cure. But that’s health care reform, like the industry its politics involve the cold calculus of high risk and trauma.