As the final round of the battle over health-care reform begins Sunday, President Obama and the Democrats are in reach of a historic legislative achievement that has eluded presidents dating back a century. The question is at what cost.

By almost any measure, enactment of comprehensive health-care legislation would rank as one of the most significant pieces of social welfare legislation in the country's history, a goal set as far back as the presidency of Theodore Roosevelt and pursued since by many other presidents. But unlike Social Security or Medicare, Obama's health-care bill would pass over the Republican Party's unanimous opposition.

Even Republicans agree on the magnitude of what Obama could pull off, while disagreeing on the substance of the legislation. Sen. Lamar Alexander (R-Tenn.) said: "Obviously, he will have achieved as president something nobody else has done. So in that sense, it's historic." But he added, "It doesn't end the health-care debate -- it just changes it. And if it does pass, it would be a historic mistake."...

Regardless of the political fallout, historians say health-care reform will take its place in the same category as the enactment of Social Security in 1935 and Medicare in 1965, and only a rung or two below passage of the major civil rights bills of the 1950s and 1960s. In addition to the bill's providing coverage for more than 32 million uninsured Americans, people would no longer be denied coverage because of preexisting conditions. The "doughnut hole" for Medicare prescriptions would eventually be eliminated, and young people could stay on their parents' insurance plan through age 26.

"I think this will be seen as a really major reform initiative," said presidential historian Robert Dallek. "How it plays out remains to be seen. But if Social Security and Medicare and civil rights are any preludes to this initiative, then I think it will become a fixed part of the national political/social/economic culture."...

At the time, President Franklin D. Roosevelt's ambitions were even larger. Historian David Kennedy, a scholar of the New Deal era, said Roosevelt originally included universal health care as part of the Social Security legislation but pulled out those provisions before sending the bill to Capitol Hill.

"He thought it was such a significant political liability it could sink the whole bill," Kennedy said.

Today, Republicans and Democrats agree on the potential significance of what could happen over the next week in Washington. Where they disagree is on the question of whether it is necessary or wise to do it....